Square Flat Washer
- Square flat washer spreads bolt-head / nut bearing on flat surfaces
- ANSI C135.22, hot-dip galvanized to ASTM A-153
- For 1/2 / 5/8 / 3/4 in bolts; 2 / 2-1/4 in square
- Prevents the nut pulling into timber or steel
- Standard under every machine-bolt nut on the line
- Thick plate for high bearing load
Technical Specifications
| Catalog | For Bolt | Size (in) | Thickness (in) | Hole (in) | Surface |
|---|---|---|---|---|---|
| RAX-SFW-12 | 1/2 in | 2 × 2 | 3/16 | 9/16 | HDG |
| RAX-SFW-58 | 5/8 in | 2-1/4 × 2-1/4 | 3/16 | 11/16 | HDG |
| RAX-SFW-34 | 3/4 in | 3 × 3 | 1/4 | 13/16 | HDG |
| Custom | Other sizes / configurations — send your conductor & structure spec | ||||
Application & Installation
Where it is used
The square flat washer spreads the bearing of a bolt head or nut over a wider area on a flat surface, stopping the fastener pulling into timber or marring steel. It is the standard washer under machine-bolt nuts across the line, sized to the bolt and thick enough for the clamping load.
Installation sequence
- Select the washer for the bolt size.
- Place it under the nut (and head if needed) on a flat face.
- Run the nut up so the washer seats flat.
- Tighten so bearing spreads across the washer.
- Confirm the washer has not dished into the surface.
Buyer’s Guide: Square Flat Washer
1. What a Square Flat Washer Does
A square flat washer is a thick steel plate with a centre hole that sits under a bolt head or nut. It spreads the clamping load over a wider area so the fastener does not crush into timber or dig into steel — the basic washer of pole-line bolting.
2. Why Square, Not Round
Square washers give more bearing area for the same nominal size and resist turning against the member as the nut runs up. ANSI C135.22 specifies the square form for pole-line machine bolts.
3. Sizing to the Bolt
Match the hole to the bolt (1/2, 5/8, 3/4 in) and the plate size to the bearing needed — larger and thicker on softwood or high load. The washer must be thick enough not to dish under the nut.
4. On Timber vs Steel
On timber the washer stops the nut pulling through; on steel it protects the surface and spreads load. Use the curved washer instead where the surface is round (a pole).
5. Galvanizing
Hot-dip galvanized to ASTM A-153 to match the bolt and last the life of the joint outdoors.
6. Pairing
Used with machine bolts, double-arming bolts and eye bolts. Order the washers with the bolts so sizes and coating match.
