Buy Square Washers Online in Australia
Square Washer Sizes — Quick Reference
Square washers have a square outer perimeter — providing larger bearing area on softer substrates like timber, where round washers would allow the bolt head to pull through. Used in timber framing, formwork, structural pole/post connections and large-bolt fastening into soft materials. AIMS stocks square washers in metric sizes, in plain mild steel, zinc yellow passivate, hot-dip galvanised and 316 stainless finishes.
| Bolt Size | Square Washer Size (Side × Thickness) | Best For |
|---|---|---|
| M10 | 40 × 3 mm | Light timber framing, deck post connections |
| M12 | 40 × 3 mm, 40 × 5 mm or 50 × 5 mm | Medium timber framing, pergola posts, fence rails |
| M16 | 50 × 5 mm, 65 × 5 mm, 65 × 6 mm or 75 × 5-6 mm | Heavy timber framing, structural post-to-beam |
| M20 | 50 × 5-6 mm or 75 × 6 mm | Large structural timber, glulam connections |
| M24 | 65 × 5 mm | Heavy structural timber and post connections |
| M30 | Hot-dip galvanised — standard size (confirm with our team) | Heavy engineered / structural steelwork connections |
Use case: ALWAYS use a square washer (not round) under a bolt head bearing on timber — round washers in timber framing risk pulling through under tension load. For coach bolts + coach screws in timber, see our coach bolts range. For round flat washers (steel-on-steel), see flat round washers. Companion: our timber fasteners range.
Square Washers for Australian Timber Framing and Structural Fastening
Square washers are flat washers with a square outer perimeter rather than the standard round profile — providing a larger bearing area on softer substrates like timber, where the larger footprint distributes bolt load and prevents the bolt head from pulling through. For Australian timber framing, structural construction, and large-bolt fastening into soft materials, square washers are the everyday choice. AIMS Industrial supplies square washers in the metric sizes Australian construction and trade users need.
Where square washers earn their place
- Timber framing and structural work — large bolts into timber where the bolt head would otherwise pull through
- Coach bolt installations — under coach bolt heads in timber connections
- Bridge and infrastructure — heavy bolt fastenings in structural applications
- Roof and ridge fastenings — where bolts pass through timber and require load distribution
- Foundation and ground-anchor work — bolted connections to soft substrates
Why square versus round washers
Round washers are the standard everyday washer — simple, inexpensive, and adequate for most fastenings into hard substrates. Square washers earn their place when:
- The substrate is soft — timber, plastic, or soft metal where load distribution matters
- The substrate has grain — timber where rotation under torque could split the substrate (the square washer's flat sides resist rotation)
- The bearing area must be larger than a standard round washer provides — for very high loads or oversized clearance holes
- The application is structural — where building codes specify washer dimensions for timber connections
Sizing
Square washer sizing has two main dimensions: the inside hole diameter (matched to the bolt size) and the outer square dimension. Sizes range from M10 through M30, with M12–M24 stocked across multiple width and thickness combinations. Thickness is typically 3mm, 5mm or 6mm, depending on bolt size and width. Match the washer to the bolt size and the load distribution requirement.
Materials and finishes
- Hot-dip galvanised steel — the standard for outdoor and timber-frame structural work
- Zinc yellow passivate steel — for indoor and protected applications
- Plain mild steel (incl. Hobkote-coated) — for paintable surfaces and where finish coatings will be applied
- 316 stainless steel — for marine and aggressive environments
Australian timber framing standards
Australian Standard AS 1684 (Residential Timber-Framed Construction) and related codes specify washer dimensions for various structural timber connections — washer outer dimensions and thickness must match the requirements for the specific connection type. For load-bearing timber connections, refer to the structural drawings and AS 1684 specifications; don't substitute smaller or thinner washers in structural applications.
Brands stocked at AIMS
Hobson covers the bulk of our square washer range — plain mild steel, hot-dip galvanised, zinc yellow passivate and Hobkote-coated finishes from M12 through M30. Inox World supplies our 316 stainless square washers, M10 through M20. Bulk packs are available for fitout and structural work; trade pack quantities for general workshop use.
Companion ranges at AIMS
Square washers sit alongside our broader fastener range — see our coach bolts range, mudguard washers, safety washers, and spring lock washers for the related products.
Need help speccing square washers for timber framing or structural work? contact our team — we'll match by bolt size, outer dimension, and material.
People Also Ask — Square Washers
Q: What's a square washer?
A square washer is a flat washer with square outer profile instead of circular — provides larger contact area than equivalent round washers for spreading bolt load over wider area. Used in timber construction (spreads load on softer timber surface), structural connections, sleeper anchoring, and any application where a larger load-spread surface is needed. Common in Australian carpentry and construction for connecting timber framing members.
Q: Square vs round washer — when to choose each?
Round washer: standard for steel-to-steel connections, lower cost, smaller footprint. Square washer: timber construction, larger load spread, used where the washer needs to span a wider area or sit flush with a square chamfered hole. Specialty applications: square hole brackets, structural timber, sleeper construction. For general workshop assembly, round washers are the standard. For carpentry and timber framing, square washers serve specific load-spreading needs.
Q: Available sizes for square washers?
Common sizes: M10 (40mm), M12 (40 or 50mm), M16 (50, 65 or 75mm), M20 (50 or 75mm), M24 (65mm), and M30 in hot-dip galvanised. Thickness is typically 3mm, 5mm or 6mm depending on size — larger bolt sizes generally run thicker. Match the centre hole diameter to the bolt size; our team can confirm the exact width/thickness combination in stock for any size.
Q: Galvanised or stainless square washers?
Hot-dip galvanised: standard for outdoor timber construction, cost-effective, 25-50 year corrosion life. Zinc yellow passivate or plain mild steel: indoor and protected applications. Stainless 316: marine, coastal and aggressive-environment exposure. Match the washer finish to the surrounding hardware and the environment. Don't mix galv and stainless — galvanic corrosion accelerates at the contact point.
Q: Do square washers come in different thicknesses?
Yes — standard thicknesses of 3mm, 5mm and 6mm are stocked, depending on bolt size. Thicker washers carry higher bolt loads and span wider load areas — larger bolt sizes (M16 and up) commonly run 5mm or 6mm, while smaller sizes are typically 3mm. The structural engineer's spec dictates the required washer thickness for any structural application.
Q: Why does a square washer resist rotation better than a round washer on timber?
Timber has grain, and rotation under torque can split the substrate. A square washer's flat sides bite into the timber surface and resist turning, whereas a round washer can spin and dig in unevenly as the bolt is tightened.
Q: What standard governs washer sizing for timber-framed structural connections in Australia?
AS 1684 (Residential Timber-Framed Construction) and related codes specify washer dimensions for various structural timber connections. Don't substitute smaller or thinner washers in structural applications — refer to the structural drawings and AS 1684 for load-bearing connections.
Q: What brands of square washers does AIMS stock?
Hobson covers the bulk of our square washer range in plain mild steel, hot-dip galvanised, zinc yellow passivate and Hobkote-coated finishes; Inox World supplies our 316 stainless square washers. Bulk packs are available for fitout and structural work, with trade pack quantities for general workshop use.
Q: Can I use a square washer on a coach bolt in timber?
Yes — square washers are the standard choice under coach bolt heads in timber connections, spreading the load over a wider area than a round washer and reducing the risk of the bolt head pulling through the timber.