Locking Assemblies

Locking assemblies — also called keyless locking devices, shrink discs, or locking elements — transmit torque from a shaft to a hub through pure friction grip, with no keyway machining required. Tightening the assembly's clamping screws forces tapered surfaces together, simultaneously expanding the hub bore outward and contracting onto the shaft. The result is a zero-backlash, infinitely-adjustable connection that handles higher torque than an equivalent keyway, installs and removes cleanly, and can be re-used.

This page covers selection by torque rating and shaft range, the differences between external (shrink disc) and internal locking patterns, correct installation and removal procedure, and the critical torque rule that prevents hub bore distortion.

Locking Assembly Selection — Quick Reference

What a Locking Assembly Actually Does

A locking assembly converts axial screw force into radial clamping force through tapered (conical) contact surfaces. As the clamping screws are tightened, the inner sleeve contracts onto the shaft while the outer sleeve expands into the hub bore. The full circumferential surface of the shaft transmits torque by friction — no key, no keyway, no point-loading.

The advantages over a traditional keyway-and-key drive are significant:

• Higher torque capacity for the same shaft diameter — friction over the entire surface beats a keyway concentrating load on one small contact patch.
• Zero backlash — there is no key-to-keyway clearance, so reversing and oscillating loads do not generate fretting wear or impact loading.
• Infinitely adjustable angular position — the hub can be timed to any rotation, not locked to a fixed keyway location.
• Clean install and removal — no broaching, no shaft damage, no pulled-out keys to chase down.
• Re-usable when cleaned and re-lubricated to the manufacturer's spec.

External vs Internal Locking — Two Different Patterns

External Locking Assemblies (Shrink Discs)

Mount externally, around the outside of the hub. The outer ring of the assembly contracts radially when its bolts are tightened, squeezing the hub onto the shaft. Used for hollow-shaft gearbox mounting, large-bore conveyor drives, and applications where you need to clamp a hub that is already in place. Sits proud of the hub OD and is visible after installation.

Internal Locking Assemblies

Mount inside the hub bore, between the shaft and the hub. The inner sleeve grips the shaft; the outer sleeve grips the hub bore. Hidden when installed. More common for standard industrial drives — gearbox input shafts, pump impellers, sprockets, V-pulleys, and timing pulleys built for keyless mounting.

Single-Taper vs Double-Taper

Single-taper assemblies use one set of conical surfaces — simpler, lower torque, lower cost. Double-taper (double-cone) assemblies use two sets of opposing tapers — clamping force is distributed uniformly around the full circumference, which both increases torque capacity for the same diameter and ensures self-centring of the hub on the shaft.

Locking Assembly vs Taper-Lock Bush — When to Step Up

Locking assemblies and taper-lock bushes are both keyless mounting solutions, but they solve different problems. Taper-lock bushes are the lower-cost workhorse for V-pulleys, sprockets, and timing pulleys at moderate torque — and they typically use a keyway in the shaft for back-up. A locking assembly is the step-up for higher torque, true zero-backlash, or where machining a keyway in the shaft is impractical (large shafts, hollow shafts, hardened shafts).

Read the full comparison in our taper-lock bush guide.

Selecting a Locking Assembly

Selection is driven by the manufacturer's technical datasheet, not by shaft diameter alone. Shaft diameter tells you which assemblies fit; torque and axial load ratings tell you which fitting assembly is adequate.

Shaft Diameter

Each assembly is rated for a specific shaft-bore range. Shaft and bore must be within the manufacturer's tolerance — typically h7 on the shaft and H8 on the hub bore. Out-of-tolerance fits change the clamping behaviour and reduce torque capacity.

Transmitted Torque + Safety Factor

The assembly's rated torque must exceed the application's working torque multiplied by a service factor. Typical safety factors:

• 1.5x — smooth, uniform loads (continuous fans, centrifugal pumps)
• 2.0x — moderate shock (mixers, conveyors with normal starts)
• 2.5-3.0x — heavy shock, frequent reversing, mining / crusher service

Axial Load Capacity

Many applications transmit both torque and axial thrust through the locking assembly. Check the axial load rating separately — it does not scale linearly with torque rating.

Hub OD and Wall Thickness

The hub must have enough wall thickness to accept the clamping pressure without yielding. Manufacturers publish minimum hub OD figures alongside the bore size — undersized hubs will deform under clamping and lose grip on the shaft.

Lubrication Specification

The relationship between bolt torque and clamping force depends on thread lubrication. Use only the lubricant specified by the manufacturer — typically MoS₂ paste or a light oil. Substituting greases changes the friction coefficient and shifts the actual clamping force away from the design value.

Installation Procedure

1. Clean every surface. Wipe shaft, bore, and the assembly itself completely free of oil, grease, and debris. Any contamination on the friction surfaces directly reduces grip — locking assemblies are designed to run dry on the clamping surfaces.
2. Lubricate the clamping screws only. Apply the manufacturer-specified lubricant to the bolt threads and under the bolt heads. Do not lubricate the tapered clamping surfaces.
3. Position the hub. Slide the assembly into the hub bore, then position the hub on the shaft to the required axial location and angular orientation.
4. Tighten in a diagonal cross-pattern in three passes — first to 30% of final torque, then 70%, then 100%. Sequential one-after-the-other tightening produces uneven clamping and reduced torque capacity.
5. Re-torque after settling. After 5-10 minutes (or after the first thermal cycle), re-check all screws to the specified final torque. The taper surfaces seat slightly during initial clamping.

Removal Procedure

1. Loosen all clamping screws progressively in the reverse of the tightening pattern. Do not remove them yet.
2. Move the loosened screws into the pull-off threads. Most locking assemblies have a set of dedicated threaded holes (clearly marked) for jacking the inner ring out of the bore.
3. Tighten the pull-off screws evenly. The inner ring will lift out of the bore and the hub releases from the shaft cleanly.
4. Inspect before re-use. Clean the friction surfaces, check for scoring or corrosion. If the surfaces are bright and intact, the assembly is re-usable. If contaminated with oil or showing wear, replace it.

Critical Torque Rule: Use the manufacturer's specified torque. Do not over-tighten "to be safe". Over-torque distorts the hub bore (and at extreme over-torque, distorts the shaft) — the immediate joint feels solid, but the deformed bore is now permanently out of round. The result is reduced fatigue life, vibration, and in heavy applications, catastrophic hub failure under load. The torque spec is engineered to develop full clamping force without bore yield. Trust the number.

Clean Surfaces Rule: Oil, grease, anti-seize, or thread-locker on the tapered clamping surfaces will reduce friction and cause the assembly to slip under load. The assembly is designed for dry, clean friction contact on the clamping faces. Lubricant goes on the bolt threads only.

Common Applications

• Heavy industrial drives — mining gearbox input/output shafts, crusher drives, conveyor head/tail pulleys, fan and blower drives.
• Hollow-shaft gearboxes — mounted directly onto the driven equipment shaft (mixer shafts, conveyor pulley shafts) using an external shrink disc.
• Precision positioning drives — printing presses, indexing tables, machine tool spindles. Zero backlash and adjustable angular position make locking assemblies the default.
• Pump impellers — keyless mounting of impellers to drive shafts, eliminating keyway corrosion concerns in chemical and water-handling applications.
• Custom and one-off industrial drives — when machining a keyway in a hardened or stainless shaft is impractical, a locking assembly avoids the need.

Locking Assemblies — Our Range

AIMS Industrial stocks shaft-hub locking assemblies in self-centring and standard internal configurations across small to large-bore shaft sizes. Common patterns we hold include:

• Type 01 Internal Locking Assembly — standard bore-mounted single-taper, general industrial.
• Type 02 Self-Centring — internal locking with auto-alignment during install.
• Type 04 Self-Centring — compact pattern for tight radial space.
• Type 07 Self-Centring — heavy-duty double-taper for maximum torque density.
• Type 19 Self-Centring — designed for disassembly under load, maintains alignment during removal.
• Large-Bore (180 x 235mm) — for shafts beyond standard ranges, heavy mining and quarry conveyor service.

If you need a size or torque rating not shown in our online range, contact our team — we source non-standard locking assemblies on quote.

Standards Reference

Locking assemblies are not formally standardised the way taper-lock bushes (ISO 13044) are — most manufacturers (Ringfeder, KTR, Tollok, Stüwe) publish their own catalogue ranges and dimensional standards. For comparison and context:

• ISO 13044 — Conical shaft ends and taper bushes for power transmission applications, including keyless locking systems. [VERIFY: current edition year]
• DIN 6885 — Parallel keys, keyways, keyed connections (the standard locking assemblies are designed to replace). [VERIFY: current edition year]

For application-specific selection — particularly the torque safety factor — refer to the chosen manufacturer's technical datasheet and the relevant equipment OEM specification.

Companion Components

Locking assemblies work in a power transmission system alongside:

• Taper-lock bushes — lower-cost keyed equivalent for V-pulley, sprocket, and timing pulley mounting at moderate torque.
• Shaft collars — axial location and stops on driven shafts.
• Couplings — flexible and rigid shaft-to-shaft connections.
• Key steel — square and rectangular keystock for backup keyway connections.
• Sprockets, V-pulleys, and timing pulleys — common driven components that mount onto locking assemblies or taper-lock bushes.
• Bearings — shaft support either side of the driven component.

AIMS' Note on Locking Assembly Selection

For accurate selection, we need the following from you:

• Shaft diameter (and tolerance class if non-standard) and hub bore diameter (and tolerance class).
• Working torque at the assembly (Nm) — including any peak / shock torque.
• Application type — uniform load, moderate shock, heavy reversing, etc. — so we can recommend a service factor.
• Axial load, if the assembly carries thrust as well as torque.
• Hub OD and wall thickness — for confirming the assembly's clamping force is supported.
• Environment — temperature, corrosive media, food/pharma compatibility if relevant.

Send these on a sketch or photo and we'll match you to the right pattern. Contact our team for application advice or request a quote.

Companion Resources

• Taper-Lock Bush Guide — when a keyed taper-lock is the better answer.
• Shaft Coupling Guide — flexible vs rigid coupling selection.
• Keyways, Keys & Key Steel Size Charts — sizing reference for backup keyed connections.

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