316 (A4) · Hardened Steel · Mild Steel
Square Washer
Square plate washers with a big flat bearing face for bolts in timber framing, decks, pergolas and steel connections.
About the Square Washer
Square washers, or plate washers, give a big flat bearing face under a bolt or set screw, for timber framing, decks, pergolas, retaining walls and oversized or slotted holes in steelwork. They come in mild steel (hot dip galvanised, plain, zinc yellow, zinc plated or Hobkote), 316 stainless, and hardened galvanised (35 to 41 HRC), from 38 x 38mm to 125 x 125mm and 3 to 16mm thick, for M8 to M42 bolts, plus XBolt square washers with an oversized hole and square hole washers. Choose the bolt size, width and thickness above; the guide below covers reading the sizes and the finish for each site.
Also called plate washers or square plate washers.
Features
- Large square bearing face
- Round and square-hole patterns
- Covers oversized and slotted holes
- Hardened options
Applications
- Bolts and set screws in timber framing
- Oversized or slotted holes in structural steelwork
- Bolted timber decks, pergolas and retaining walls
What square washers do
Hobson describes a standard washer as a thin plate, typically round or square, with a hole that is normally in the centre. It does two jobs:
- It stops the nut scouring or scratching the surface it bears on as it is turned.
- It increases the bearing surface of the bolt or nut, spreading the load of the fastener over a larger area so the bearing surface does not deform.
Why a square washer instead of a round one
- A square washer gives a larger bearing surface than a round washer, and its flat edges and greater contact friction resist turning while you tighten the nut.
- Hobson lists square washers for bolts and set screws in timber framing, and for covering oversized and slotted holes in bolted connections and structural steelwork.
How to choose a square washer
- Bolt size: the washer is named for the bolt it fits. An M12 square washer has a 13mm hole for an M12 (12mm) bolt; the hole for each size is in the table below.
- Width: how far the plate spreads the load. Our square washers run from 38 x 38mm up to 125 x 125mm. Where your plans or engineer give a washer size, use that size.
- Thickness: from 3mm up to 16mm. A thicker plate is stiffer, and the thicker plates come in the larger bolt sizes and widths.
- Finish: match the bolt and nut, and the exposure (see the finishes section). Hot dip galvanised or stainless outdoors, zinc only indoors or under cover.
- Special types: hardened square washers for high tensile bolting in steelwork, XBolt washers with an oversized hole for XBolt screw bolts, and square hole washers. Tapered (8 degree) square washers are on our taper and Sampson washer page, linked at the foot of this page.
Square washer sizes: M8 to M42 in every finish
Every standard square washer we carry, by bolt size. Select a size to open it in the selector, then pick the finish, width and thickness. XBolt and square hole washers are in the next table.
Hobson's hardened washer sheet gives the hardened washers a slightly larger hole (17.3mm for M16, 21.3mm for M20, 38.4mm at M36).
Width x thickness in mm (the plate is square, so 50 x 3 is a 50 x 50mm plate, 3mm thick), from our product data. Hole is the hole diameter in mm for the hot dip galvanised washers, from Hobson's hot dip galvanised sheet (M42 is not on it). A blank cell means we do not carry that size in that finish. Min. order runs from 200 (thin 38 to 50mm plates) down to 10 (the largest and thickest plates); the selector shows each. Tap a number to show it in the selector above.
| Bolt size | Hole (mm) | Hot dip galvanised | Plain | Zinc yellow | Zinc plated or Hobkote | 316 stainless | Hardened galvanised (35 to 41 HRC) |
|---|---|---|---|---|---|---|---|
| M8 | 9 | 38 x 3 | |||||
| M10 | 11 | 38 x 3, 38 x 5, 50 x 3, 50 x 5, 50 x 6 | 50 x 3, 50 x 5 | 38 x 3, 50 x 3 | 50 x 3, 50 x 6 | ||
| M12 | 13 | 38 x 3, 38 x 5, 50 x 3, 50 x 5, 50 x 6, 65 x 5, 65 x 6, 75 x 5, 75 x 6 | 40 x 5, 50 x 3, 50 x 5, 65 x 5 | 50 x 3, 50 x 5 | 50 x 3, 50 x 5 (Hobkote) | 50 x 3, 50 x 6, 75 x 6 | |
| M14 | 15 | 50 x 3 | 50 x 3 (Hobkote) | ||||
| M16 | 17 | 50 x 3, 50 x 5, 50 x 6, 65 x 5, 65 x 6, 75 x 5, 75 x 6, 75 x 10, 100 x 10 | 50 x 5, 50 x 6, 65 x 6, 75 x 5, 75 x 6 | 50 x 5, 65 x 5 | 50 x 3 (zinc), 50 x 5 (Hobkote) | 50 x 3, 50 x 5, 50 x 6, 65 x 10 | 50 x 10, 60 x 4 |
| M20 | 21 | 50 x 3, 50 x 5, 50 x 6, 65 x 5, 65 x 6, 75 x 5, 75 x 6, 75 x 8, 75 x 10, 100 x 6, 100 x 8, 100 x 10, 100 x 12, 125 x 5 | 50 x 6, 65 x 6, 75 x 6 | 50 x 5, 50 x 6, 75 x 10, 125 x 5 | 60 x 4 | ||
| M24 | 25 | 65 x 5, 65 x 6, 75 x 5, 75 x 6, 75 x 8, 75 x 10, 100 x 6, 100 x 8, 100 x 10, 100 x 12 | 65 x 5 | 75 x 6, 75 x 12, 90 x 10 | 60 x 4, 65 x 4 | ||
| M30 | 31 | 75 x 5, 75 x 6, 75 x 8, 75 x 10, 75 x 16, 90 x 10, 100 x 6, 100 x 8, 100 x 10, 100 x 12 | 75 x 5, 75 x 6, 90 x 12 | 60 x 4, 75 x 6 | |||
| M36 | 38 | 75 x 8, 100 x 6, 100 x 8, 100 x 10, 100 x 12 | 100 x 6, 100 x 16 | 75 x 6 | |||
| M42 | 100 x 8 |
XBolt square washers and square hole washers
XBolt square washers have an oversized hole to fit over the larger thread of XBolt screw bolts (concrete screws). Hobson gives their main use as securing timber frame bottom plates to concrete slabs. Square hole washers have a square hole in place of a round one; the hole size is in the description of each washer.
Width x thickness in mm from our product data. Hole in mm from Hobson's XBolt washer sheets and the square hole washer descriptions. Min. order is per size. Tap a number to show it in the selector above.
| Type and bolt size | Width x thickness | Hole (mm) | Min. order |
|---|---|---|---|
| XBolt, hot dip galvanised, M10 | 38 x 3, 50 x 3 | 13 round | 200 |
| XBolt, hot dip galvanised, M12 | 50 x 3 | 15 round | 200 |
| XBolt, zinc yellow, M10 | 50 x 3 | 13 round | 200 |
| XBolt, zinc yellow, M12 | 50 x 3 | 15 round | 200 |
| Square hole, hot dip galvanised, M10 | 40 x 3 | 11 square | 200 |
| Square hole, hot dip galvanised, M12 | 40 x 3, 50 x 3, 50 x 5 | 13 square | 100 to 200 |
| Square hole, hot dip galvanised, M16 | 50 x 3, 50 x 5, 65 x 5, 75 x 5 | 17 square | 50 to 100 |
| Square hole, hot dip galvanised, M20 | 50 x 5, 75 x 6 | 21 square | 50 to 100 |
Hardened square washers for high tensile bolting
Hobson's hardened square washers are hot dip galvanised and through hardened to 35 to 41 HRC. Its sheet lists them as suitable for high tensile bolting, for use with oversized or slotted holes drilled in steelwork, and made in sizes to state-based department of transport specifications. We carry M16 to M36, 50 to 75mm wide. Use them with the bolts, nuts and washer arrangement the steelwork drawings specify.
Square washer finishes: indoors, outdoors and on the coast
From Hobson's finish comparison, its corrosion guide for metal connectors and its square washer sheets. The corrosion guide treats decks, pergolas and open sub-floors as exposed: there it calls for hot dip galvanised or 304 or 316 stainless in low, coastal and industrial zones, stainless in the sea spray zone, and 316 stainless within 2m of a pool edge. Zinc finishes are for enclosed or dry indoor work.
- Hot dip galvanised: a 50 micron coating with high corrosion resistance, recommended for long term outdoor work. Newer galvanising is a duller grey than it used to be; Hobson notes the brightness has no effect on performance.
- 316 stainless: for coastal and poolside work. Even 316 can show surface marks where salt spray is left to build up, so rinse it with the rest of the structure.
- Hobkote: Hobson's low tensile coating, 5 to 8 microns with a specially formulated passivation, which Hobson says gives 33% more corrosion resistance than zinc plating. It is still a thin electroplated coating to ISO 4042, the same standard as zinc plating, so keep it to enclosed work; for exposed work use hot dip galvanised or stainless.
- Zinc yellow passivate: 5 microns with a yellow passivate, more corrosion resistant than zinc plated, for low corrosion conditions or temporary fixing.
- Zinc plated: 5 microns with a clear passivate, for indoor and non-corrosive conditions.
- Plain: no coating, supplied lightly oiled. Hobson lists plain square washers for structural steelwork, crusher plants and anywhere welding is required, as the plain finish lets you apply the coating of your choice.
Fitting square washers
- Match the washer to the bolt diameter, and use the same finish as the bolt and nut so one part does not corrode first.
- Put a washer under the nut, the part you turn, and under the bolt head too where it bears on timber or covers an oversized or slotted hole.
- Make sure the whole plate sits flat on the surface, then tighten the nut to the bolt's specification.
Square washers on decks, pergolas and posts
Bolted timber joints on decks, pergolas and posts are exposed, so use hot dip galvanised or stainless square washers with bolts and nuts in the same finish (316 stainless near the sea or a pool). Hobson publishes no load or capacity figures for these washers, so the bolt size, washer size and number of bolts for a structural joint come from your plans, the bracket maker or an engineer, not from this page.
Square washers in Adelaide
Allmat supplies square washers, bolts, nuts and threaded rod to builders, carpenters, fabricators and trade across Adelaide and South Australia. Add the washers to a quote with the bolts and nuts they go on, and we will price the lot.
Square washers, bolts and nuts for the job
Galvanised, zinc, plain, stainless and hardened square washers, with the bolts, nuts and threaded rod they go on, are available to order from Allmat for builders, carpenters, steel fabricators and trade across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.
Goes with
Questions
What is a plate washer?
Another name for a square washer: a flat square steel plate with a hole in the centre. It gives a larger bearing surface than a round washer and its flat edges resist turning while the nut is tightened.
What size square washer for an M12 bolt?
An M12 square washer, which has a 13mm hole. We carry M12 square washers from 38 x 38mm to 75 x 75mm and 3 to 6mm thick; the everyday one is 50 x 50 x 3mm hot dip galvanised, in packs of 200.
What is the difference between a square washer and a round washer?
A square washer gives a larger bearing surface than a round washer of the same size, and its flat edges and greater contact friction resist turning during tightening. Hobson lists square washers for timber framing and for covering oversized and slotted holes in steelwork.
Can I use galvanised square washers on a deck or pergola?
Yes. Hobson's corrosion guide treats decks and pergolas as exposed and lists hot dip galvanised or 304 or 316 stainless for exposed work in low, coastal and industrial zones; in the sea spray zone use stainless, and within 2m of a pool edge 316 stainless. Hobson publishes no load figures for these washers, so take the bolt and washer sizes for a structural joint from your plans or engineer.
What are XBolt square washers for?
They have an oversized hole (13mm for M10, 15mm for M12) to fit over the larger thread of XBolt screw bolts. Hobson gives their main use as securing timber frame bottom plates to concrete slabs.
What are hardened square washers used for?
High tensile bolting in steelwork. Hobson lists its hot dip galvanised hardened square washers at 35 to 41 HRC, for use with oversized or slotted holes drilled in steelwork, made in sizes to state-based department of transport specifications.
Do you have tapered square washers?
Yes, 8 degree tapered square washers are on our taper and Sampson washer page, linked at the foot of this page.
Where can I buy square washers in Adelaide?
Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.
Square Washer: sizes and finishes we supply
135 lines by type and finish. Pick one above for its product code, pack sizes and dimensions.
| Type | Finish | Sizes | Lengths | Lines |
|---|---|---|---|---|
| Standard | Galvanised | M8, M10, M12, M14, M16, M20, M24, M30, M36, M42 | x38x3 to x125x5 (18 lengths) | 68 |
| Standard | 316 Stainless | M10, M12, M16, M20, M24, M30, M36 | x50x3 to x125x5 (13 lengths) | 21 |
| Standard | Steel | M10, M12, M16, M20, M24 | x40x5, x50x3, x50x5, x50x6, x65x5, x65x6, x75x5, x75x6 | 15 |
| Square hole | Galvanised | M10, M12, M16, M20 | x40x3, x50x3, x50x5, x65x5, x75x5, x75x6 | 10 |
| Standard | Zinc Yellow Passivate | M10, M12, M16 | x38x3, x50x3, x50x5, x65x5 | 8 |
| Hardened | Galvanised | M16, M20, M24, M30, M36 | x50x10, x60x4, x65x4, x75x6 | 8 |
| Standard | Hobkote | M12, M14, M16 | x50x3, x50x5 | 4 |
| Standard | Zinc Plated | M16 | x50x3 | 1 |
Data sheets and documents
The documents for the product you choose are listed with the selector above. Here is every Square Washer document from Hobson Engineering.
All Square Washer documents (15)
Data sheets and technical data (4)
Did You Know flyers (7)
Need them in bulk?
Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.
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