Bearings & Power Transmission Guide: Types & Selection

Bearings and power transmission components are the parts that keep machines turning. Get the selection right and your gear runs quietly for years. Get it wrong and you'll be back at the gearbox, the conveyor or the motor mount within weeks. This guide is the orientation map. It covers what each component does, where it fits, how to identify it, and which AIMS range to look at. For depth on any one topic — sizing a taper-lock bush, decoding a 6203 bearing number, picking a coupling, measuring a V-belt — we link out to the specialist guide.

Use the Quick Reference table immediately below to jump to the right section. If you're after a specific bearing or component and just need to talk to someone, the Sydney sales desk is on (02) 9773 0122 — bring your old part number, shaft size or housing dimensions and we'll work it out from there.

Bearings & Power Transmission — Quick Reference

Bearing Categories Explained

A bearing's job is to carry load between two parts that move relative to each other — usually a rotating shaft and a stationary housing — with minimum friction. Bearings split into two big families: rolling-element bearings (balls or rollers between two races) and plain bearings (a sleeve of low-friction material running directly on the shaft). Within rolling-element bearings, the choice of element (ball vs roller) and its geometry tells you what kind of load it carries.

Ball bearings

Balls have very low rolling friction but contact the races at a single point, so their load capacity is lower than a roller bearing of the same size. Ball bearings dominate light-to-medium industrial applications — electric motors, pumps, fans, small gearboxes, machine spindles.

• Deep groove ball bearings — the workhorse type. The deep raceway carries radial load and a moderate amount of thrust in either direction. The numbers most engineers know (6203, 6204, 6205) are deep groove ball bearings. Available open, shielded (ZZ) or sealed (2RS). See our Deep Groove Ball Bearing Guide for sizing and selection.
• Angular contact ball bearings — the inner and outer races are offset so the ball contact line runs at an angle (15°, 25°, 30°, 40°). This gives much higher thrust capacity in one direction. Used in pairs for spindles, pumps and machine tools. AIMS stocks them under Angular Contact Bearings.
• Self-aligning ball bearings — two rows of balls running in a spherical outer raceway. Tolerates shaft misalignment up to a few degrees. Useful for long shafts in agricultural and conveyor work where housings can't be precisely aligned.
• Thrust ball bearings — designed for axial load only. The races sit perpendicular to the shaft. Used on turntables, lazy susans, low-speed vertical shafts. See Thrust Bearings & Washers and the dedicated Thrust Bearing Guide.

Roller bearings

Rollers contact the race along a line rather than a point. That spreads load over a larger area and gives a roller bearing several times the radial load capacity of a ball bearing of the same envelope size. The trade-off is friction (slightly higher) and sensitivity to misalignment.

• Cylindrical roller bearings — straight rollers, very high radial load capacity, can accommodate axial shaft expansion. Used in gearboxes, electric motors above ~10 kW, traction motors. Australian range: Cylindrical Roller Bearings.
• Spherical roller bearings — barrel-shaped rollers in a spherical outer raceway. Heavy radial plus moderate axial load, tolerates misalignment. The standard choice for vibrating screens, crusher shafts, large fans, heavy conveyors. Spherical Roller Bearings.
• Tapered roller bearings — conical rollers, carry combined radial and thrust load. Almost always installed as a pair to take thrust in both directions. Wheel hubs, pinion shafts, vertical pump shafts. Tapered Roller Bearings.
• Needle roller bearings — small-diameter rollers with high length-to-diameter ratio. Very compact in the radial direction. Used in universal joints, rocker arms, gearbox planetary stages, motorcycle small ends. Drawn-cup and machined-ring versions stocked at Needle Roller Bearings. The Needle Roller Bearing Guide covers shaft hardness requirements and selection.

Plain bearings and bushings

A plain bearing has no rolling elements — just a sleeve of low-friction material (bronze, oilite, polymer, PTFE-impregnated) that the shaft turns inside. They're cheap, take up almost no radial space, run quieter than rolling bearings and tolerate dirt and shock. The trade-off is friction (higher), heat generation and a strict need for lubrication or self-lubricating material.

• Bronze bushes — solid bronze, often grooved for grease. Heavy-duty oscillating loads — pin joints, hinge points, low-speed shafts.
• Oilite (sintered bronze) — porous bronze pre-impregnated with oil. Self-lubricating for the life of the bearing in light-duty rotary use.
• Polymer / PTFE-lined — quiet, dry-running, food-grade options available. Good for low loads where grease is not allowed.

Full range at Bushings. Note: "bushing" and "bush" mean the same thing — Australian usage is mostly "bush", US is "bushing".

Linear bearings

So far we've talked about bearings for rotary motion. Linear bearings carry load on shafts or rails that slide linearly — machine tool axes, automation rails, packaging machines, sliding doors. Three common types: linear ball bushings on round shafts, linear roller blocks on profile rails, and plain linear sleeves (often polymer). See the Linear Bearing Guide for selection.

Bearing Housings — Pillow Blocks, Flanges and Take-Ups

Most rolling-element bearings need a housing to mount them to a structure. The housing protects the bearing, holds it in alignment and provides the bolt pattern for fixing. AIMS calls these mounted bearings or bearing units. The bearing inside is usually a self-aligning insert (UC-series) with an eccentric collar or grub-screw lock.

FYH is one of the strongest brands for mounted bearings in Australia — light cast-iron and stainless ranges, both well-stocked. See FYH and the broader Bearing Housings range. For replacement and installation guidance, see the Pillow Block Bearing Guide.

Decoding ISO Bearing Numbers

Most bearings carry an ISO part number that tells you the type, size and features without needing a catalogue. The system is standard across SKF, NSK, Koyo, Nachi, NTN, FAG and most other reputable makers — a 6205-2RS is a 6205-2RS from any of them, although seal materials and internal clearance can differ.

The number breaks down like this: [Series][Bore]-[Suffix].

• First digit (or two) — bearing type and series. 6 = single-row deep groove. 7 = angular contact. 22 / 23 = spherical roller. 32 / 33 = tapered roller. NU / N / NJ = cylindrical roller variants. NA / RNA = needle roller.
• Next digit — width / diameter series (how "fat" the bearing is). 0 / 2 = light, 3 = medium, 4 = heavy. So a 6203 is light-series, a 6303 is the same bore but a medium-series with larger OD and higher load rating.
• Last two digits — bore code. For codes 04 and above, multiply by 5 to get the bore in mm. So 6203 = 17 mm bore. 6204 = 20 mm. 6205 = 25 mm. 6206 = 30 mm. Codes 00–03 are the exceptions: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm.
• Suffix — seals, shields, clearance, cage. ZZ / 2Z = metal shield both sides. 2RS = rubber seal both sides. C3 = larger-than-standard internal clearance (for hot or interference-fit applications). C2 = smaller. P5 / P6 = precision class.

Worked example: 6205-2RS C3 is a single-row deep groove ball bearing, light series, 25 mm bore, rubber sealed both sides, C3 clearance. Quick reference cards for the full bore code list and equivalent codes across brands live in our Bearing Cross-Reference Guide.

Belts — V-Belts, Synchronous and Banded

A belt drive transmits power between two pulleys using friction (V-belt) or positive engagement (synchronous / timing). Compared to chain or gear drives, belts run quieter, need no lubrication, and absorb shock — but they slip under heavy overload and need re-tensioning every few thousand hours.

V-belts

The wedge-shaped V-belt is the workhorse of industrial drives. Two families: classical (A, B, C, D, E — wider, thicker, slower) and narrow / wedge (SPZ, SPA, SPB, SPC — smaller cross-section, higher power per unit width). Cogged or notched versions allow smaller pulley diameters and stay cooler.

• Classical (A / B / C) — pumps, fans, compressors, general industrial.
• Narrow (SPZ / SPA / SPB / SPC) — same power in a smaller package — modern preferred standard.
• Banded (matched set joined at the top) — high-vibration drives where single belts would whip and roll out.

For sizing, measurement (outside vs effective length, inch vs SPC) and how to read the belt code, see How to Measure a V-Belt. Gates is the dominant brand in Australia — full range at Gates. Browse the broader Belts range.

Synchronous (timing) belts

Synchronous belts have moulded teeth that mesh with grooved pulleys, so there is no slip — the input and output rotate in fixed ratio. Used wherever timing matters: engine cams, CNC indexing axes, positioning conveyors. Tooth profiles include classical (L, H, XH), modern HTD / GT (curvilinear) and metric T / AT. Specifications and pitch tables in the Synchronous Timing Belt Guide.

FRAS and heavy-duty belts

For underground coal, food processing and high-shock mining drives, special compounds are required — fire-resistant anti-static (FRAS) and heavy-load aramid-reinforced. AIMS supplies Gates Predator and Banded Predator ranges for those use cases.

Chain Drives

Roller chain is the positive-drive workhorse where a belt would slip — heavy conveyors, packaging lines, motorbikes, agricultural machinery. Standard chain in Australia comes in two pitch systems:

• ANSI (American) — sizes 25, 35, 40, 50, 60, 80, 100, 120, 140, 160, 180, 200. The first digit times 1/8" gives the pitch. So 40 = 1/2" pitch, 60 = 3/4" pitch, 80 = 1" pitch.
• BS / ISO (British) — sizes 06B, 08B, 10B, 12B, 16B, 20B, 24B etc. 08B = 1/2" pitch. Slightly different roller / plate dimensions to ANSI even at the same pitch — not interchangeable.

Variants include simplex (single strand), duplex (two), triplex (three), heavy-duty plate, stainless and self-lubricating. Sprockets must match the chain pitch and number of teeth needed. Full range at Chain & Sprockets. Roller chain sizing, lubrication, tensioning and replacement in the Roller Chain Guide; tensioner selection in the Chain Tensioner Guide.

Couplings — Connecting Shafts

A coupling joins a driving shaft (usually a motor) to a driven shaft (pump, gearbox, fan) so torque transfers but small misalignments don't destroy the bearings. Choose by the kind of misalignment you need to handle and the level of damping you need.

Range at Couplings. For sizing, bore and balance specs see Shaft Coupling Guide and Flexible Coupling Guide. Shaft Collars hold components axially in place — separate item to couplings.

Pulleys

A pulley is the wheel that a belt runs on. Three groups depending on what belt:

• V-pulleys — grooved for V-belts. Sizes specified by pitch diameter and number of grooves. Common SPA / SPB / SPC grooves. V Pulleys.
• Timing pulleys — toothed for synchronous belts. Specified by tooth profile (L, H, HTD-5M, HTD-8M, GT3 etc.), number of teeth and bore. Timing Pulleys.
• Idler / tensioner pulleys — smooth or grooved wheels that take up slack and route belts around obstacles. Mounted on adjustable arms.

Browse the full Pulleys range. To calculate driven speed when you change pulley sizes, use the formula and worked example in Pulley Speed Ratio. For an overview of every pulley type with selection guidance, see Pulley Types Guide.

Sprockets

A sprocket is the toothed wheel that drives a roller chain. Specified by chain pitch (matches the chain — 06B, 08B, 40, 50, 80 etc.), number of teeth, hub style (plate / B-hub / taper-lock) and bore. AIMS stocks plate, simplex, duplex and triplex sprockets and matching taper-lock variants under Sprockets.

Quick selection notes:

• More teeth = smoother running, less wear, but larger drive.
• Don't go below 17 teeth on high-speed drives — chain articulation angle becomes too aggressive.
• Match pitch exactly — a 50-pitch chain will not run on a 40-pitch sprocket.
• Hardened-tooth versions last 3–5× longer in abrasive / loaded service. Worth the upcharge.

Taper-Lock Bushes

A taper-lock bush is a split tapered sleeve that lets you mount a pulley, sprocket or coupling onto a plain shaft (no keyway) using just three set screws. The bush wedges into the matching taper bore in the pulley as the screws pull. Removal is just as quick — back the screws out, drop one into the threaded jacking hole, and the bush releases.

The standard taper-lock series (Fenner-type, used worldwide) runs from 1008 (smallest) up to 5050 (largest). The first two digits are the bush outside diameter in inches × 10, the second two are the bush length in inches × 10. So a 2517 bush is 2.5" OD by 1.7" long.

Bushes are bored to a specific shaft size — 1008/12 means a 1008 bush with a 12 mm bore. Stock common shaft sizes; less common bored on demand. Range at Taper Lock Bushes; full sizing tables, installation torque and removal procedure in the Taper Lock Bush Guide.

Key Steel and Keyways

Where you can't use a taper-lock bush — usually because the shaft already has a keyway — a parallel key locks the pulley, sprocket or coupling to the shaft. The key sits half in the shaft keyway and half in the pulley keyway, transferring torque by shear.

• Parallel key — most common. Rectangular cross-section to ISO 2491 / AS 2938. Cut to length from key steel stock.
• Woodruff key — half-moon shape, sits in a milled semi-circular slot. Used where the shaft can't accept a full-length keyway (small / tapered shafts, motor shaft ends).
• Gib-head key — has a head for removal. Used in heavy industrial where the key is fitted for life.

AIMS stocks parallel key steel in metric and imperial sizes — Key Steel.

Lubrication Basics

Bearings fail from lubrication problems more often than from any other cause — too little, too much, the wrong type, or contamination getting in. The decisions are simple, the discipline isn't.

Grease vs oil

• Grease — easiest to apply, stays where you put it, also acts as a seal against contamination. Used for ~90% of industrial rolling bearings. Lithium-complex NLGI 2 is the general workshop standard.
• Oil — used where heat is too high for grease (above ~120 °C continuous), where speeds are very high, or where the bearing is part of a circulating lubrication system already supplying the gearbox.

Sealed vs open bearings

• Sealed (2RS) — rubber lip seal, grease pre-packed at manufacture, life-of-bearing. Cannot be regreased.
• Shielded (ZZ) — metal shield, light contact. Grease pre-packed but can be displaced over time.
• Open — relies on the housing or external system for lubrication. Regreased on a schedule.

Regreasing intervals

Industry rule of thumb is hours-of-operation based, calculated from shaft speed, bearing bore and operating temperature. For most workshop installations, 6–12 months is a reasonable starting interval — adjusted shorter for high-temperature or contaminated environments. Use no more than the bearing housing volume; over-greasing causes heat and seal failure. For the full intervals table and grease selection, see the Bearing Maintenance Guide.

Selection Criteria — What to Tell Us When You Call

If you know the existing bearing number we can quote off it in seconds. If it's a clean-sheet selection — replacing a worn-out unit with no markings, or designing-in for a new build — work through these:

1. Load — radial, thrust, combined. A pump shaft has mostly radial load. A vertical mixer shaft has thrust. A wheel hub has both.
2. Magnitude. Static and dynamic load ratings on the data sheet are quoted in newtons (N) or kilonewtons (kN). For most workshop work, the existing bearing's rating tells you what's been working — match or exceed.
3. Speed (RPM). Each bearing has a limiting speed. Sealed bearings, larger sizes and heavy-grease lubrication all reduce it.
4. Operating temperature. Standard bearings work to ~120 °C. Above that, special heat-treatment (S0, S1) and high-temp grease are needed.
5. Environment. Wet? Dusty? Food-contact? Stainless inserts, FDA-grease, special seals all come into play.
6. Mounting space. The available envelope (bore, OD, width) often dictates the series. A 25 mm bore can run a 6005 (light), 6205 (medium) or 6305 (heavy) — pick by load needed in the OD you have.
7. Life expectancy. L10 life is the hours at which 10% of identical bearings would fail. Industrial standard is 20,000–40,000 hr. Quality cost lifts L10 — cheap bearings have lower L10 ratings.

Brand Selection — SKF, NSK, Koyo, Nachi, NTN, FYH

All six premium brands AIMS stocks meet ISO standards and are interchangeable on dimension. What differs is consistency, internal clearance grading, seal quality and grease type. Quick orientation:

• SKF (Sweden) — global benchmark. Premium-priced, full range, strongest in heavy industry, marine and mining. SKF range.
• NSK (Japan) — premium tier alongside SKF. Particularly strong in automotive and machine tool spindles. NSK range.
• Koyo (Japan / JTEKT) — Toyota's house brand, very strong on tapered rollers and automotive applications, good value premium tier. AIMS stocks 120+ Koyo lines — Koyo range.
• Nachi (Japan) — strong on deep-groove ball and angular-contact, popular in machine tool and pump rebuilds. 169 lines at AIMS — NACHI range.
• NTN (Japan) — full range, particularly strong on cylindrical and tapered rollers. NTN range.
• FYH (Japan) — specialist in mounted bearings (pillow blocks, flange units). Wide stainless and food-grade range. Australia's go-to for conveyor units. FYH range.

For drive components, Gates dominates the Australian belt market — Gates range. AIMS holds 431 Gates lines.

Note on "no-name" bearings: low-cost imports from non-tier-1 sources are tempting for short-life or low-criticality applications. For anything safety-critical or where downtime cost is significant, the premium-brand upcharge is small compared to a premature failure.

Australian Standards & ISO References

• ISO 15:2017 — rolling bearings, radial bearings, boundary dimensions..
• ISO 5593 — rolling bearings vocabulary.
• ISO 76 / ISO 281 — static load rating / dynamic load rating & L10 life calculation.
• ISO 5753 — radial internal clearance classes (C2, CN, C3, C4, C5).
• AS 2938 — keys and keyways, metric series.
• ISO 4156 / DIN 5480 — involute splines (for higher-torque shaft connections).
• AS 1403 — design of rotating steel shafts. AS 1403-2004 (R2016) — design of rotating steel shafts. Referenced for shaft sizing under combined bending and torsion..

AIMS' Note on Bearing & Power Transmission Sourcing

Two things make bearing and PT sourcing slower than it should be: missing part numbers and incomplete shaft / housing dimensions. If you ring the AIMS sales desk on (02) 9773 0122 with any of the below already in front of you, we can usually quote within minutes:

• Existing bearing number off the seal face or outer race (e.g. "6205-2RS" or "22209 EK").
• For mounted bearings: housing code (UCP / UCFL etc.) and shaft size.
• For belts: code stamped on the back of the belt (e.g. "SPB 1800" or "B49") OR centre-to-centre distance plus pulley pitch diameters.
• For chains: pitch (or ANSI / BS chain number) plus required length or pitches.
• For couplings: motor shaft diameter + driven shaft diameter + estimated torque (or motor kW + RPM).
• For taper-lock bushes: pulley / sprocket bore size and required shaft bore.

If you can't find a number — bearing badly worn, oily, half-buried in housing — measure ID, OD and width with a vernier. Three measurements gets us 95% of the way to the right part.

Frequently Asked Questions

What does the number 6203 mean on a bearing?

6203 is a single-row deep groove ball bearing, light series, with a 17 mm bore. The 6 = deep groove ball. The 2 = light width series. The 03 = 17 mm bore (bore code 03 is one of the legacy exceptions; from code 04 upwards, multiply by 5 to get the bore in mm). A 6203-2RS adds rubber seals both sides; a 6203 ZZ adds metal shields. Any reputable maker (SKF, NSK, Koyo, Nachi, NTN) makes interchangeable 6203s.

What's the difference between a ball bearing and a roller bearing?

A ball bearing uses spherical balls between the inner and outer race, so contact is essentially a point. A roller bearing uses cylindrical, tapered, spherical or needle-shaped rollers — contact is a line. Line contact carries 2–5× more radial load than point contact of the same size, but rollers have slightly higher friction and are more sensitive to misalignment. Use ball bearings for high speed and moderate load; use roller bearings for heavy load.

What does 2RS mean on a bearing?

2RS means the bearing has rubber lip seals on both sides — pre-greased and intended for the life of the bearing without regreasing. ZZ (sometimes 2Z) means metal shields both sides — non-contact, lower friction, but less effective seal against moisture. "Open" or no suffix means no seal — relies on the housing or external lubrication.

How do I work out a bearing's bore size from its number?

For codes 04 and above: multiply the last two digits by 5. So 6204 = 20 mm bore, 6205 = 25 mm, 6206 = 30 mm, 6220 = 100 mm. Codes 00–03 are exceptions: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm. Below 00, the bearing is a miniature series (e.g. 625 = 5 mm bore, 626 = 6 mm) where the last digit is the bore in mm.

Are SKF, NSK and Koyo bearings interchangeable?

On dimensions, yes — they all follow ISO 15. A 6205 from any of them fits the same shaft and housing. Internal clearance is also standard (C2 / CN / C3 / C4). What differs is grease type, seal compound, manufacturing tolerance class and cage material. For most workshop replacements, any of the tier-1 brands will work. For high-precision machine spindles or vibration-sensitive applications, stay within one brand and clearance class.

What's a pillow block bearing?

A pillow block is a self-aligning bearing pre-mounted in a cast-iron (or stainless / pressed steel) housing with two mounting feet. The bearing inside is locked to the shaft with grub screws or an eccentric collar; the housing bolts down to a horizontal surface so the shaft runs parallel to the floor. UCP-series (cast iron) is the most common — UCP204, UCP205, UCP206 etc. Used everywhere on conveyors, fans, augers, agricultural equipment.

What's the difference between a V-belt and a timing belt?

A V-belt is wedge-shaped and transmits power by friction against grooved pulleys — it can slip under overload (a useful safety feature) and doesn't maintain timing between the driver and driven. A timing (synchronous) belt has moulded teeth that engage matching grooved pulleys — no slip, fixed ratio, used wherever positional timing matters (engine cams, CNC indexing, positioning conveyors). V-belts run cheaper and absorb shock better; timing belts give precision.

What is a taper-lock bush?

A taper-lock bush is a split tapered sleeve that wedges into a matching taper bore in a pulley, sprocket or coupling — using three set screws — to lock the component to a shaft without needing a keyway. Quick to fit, quick to remove (back the screws into the jacking thread), reusable. Sizes run 1008 to 5050; the first two digits are bush OD in inches × 10 and the last two are length in inches × 10.

How do I know which size taper-lock bush I need?

The pulley or sprocket data sheet specifies the bush size — they're made to fit specific bush series. From there you order the bush with a bore matching your shaft. Example: "SPB 200 × 2 bush 2012" means you need a 2012-series taper-lock bush bored to your shaft diameter (the bush bore is specified separately, e.g. 2012/25 = 25 mm bore). For full sizing tables, see the Taper Lock Bush Guide.

What's C3 clearance and when do I need it?

Bearings ship with a range of internal radial play (the small gap between the rolling element and the races). CN (normal) is standard. C3 is wider — used when the inner race will be a tight interference fit on the shaft (which closes up clearance), when the bearing will run hot (thermal expansion closes clearance), or for electric motor applications. C2 is tighter. C4 / C5 are progressively wider for very heat-affected applications. If you can't find the original spec, CN is the safe default for general repair work; C3 for electric motors.

Can I mix bearing brands on the same shaft?

For most workshop applications, yes — fit dimensions are identical across reputable brands. For machine tool spindles, vibration-sensitive precision equipment, or paired angular-contact bearings (where the matched pre-load matters), stay within one brand and one clearance class.

How often should I regrease a pillow block bearing?

Industry rule of thumb is 6–12 months for general workshop / conveyor use; 1–3 months for hot, dusty or wet environments; 1–2 weeks for severe service. Use lithium-complex NLGI 2 grease unless the operating temperature is above 120 °C or there's chemical / food-contact requirements. Pump until you see clean grease coming out the relief port (or two strokes if there's no relief). Don't over-grease — full housings cause heat and seal failure.

What's the difference between a coupling and a shaft collar?

A coupling joins two separate shafts together so torque transfers from one to the other (motor shaft to pump shaft, for example). A shaft collar locks a component (pulley, sprocket, sensor disc) at a specific axial position on a single shaft — it doesn't transfer torque between shafts.

How do I choose between a chain drive and a belt drive?

Belt drives run quieter, need no lubrication, absorb shock, and are easier on the bearings — but they slip under heavy overload and lose tension over time. Chain drives are positive (no slip), carry more power per unit width, and last longer in heavy or shock-loaded service — but they're noisier, need lubrication and are sensitive to misalignment. Rough rule: belts for under-30 kW general industrial, fans, pumps and machine drives; chain for heavy conveyors, agriculture, motorcycles and any drive where slip would cause damage.

What's the most common bearing failure?

Lubrication-related — too little grease, wrong grease, contamination ingress, or over-greasing causing heat. The visible failure mode is usually pitting / spalling on the raceway. Other causes: misalignment (uneven wear pattern), shock load (race fracture), and electrical pitting from VFD-driven motors without insulated bearings or shaft-grounding (frosted appearance on the race). See the Bearing Maintenance Guide for full failure-mode photos and diagnosis.