Select a preliminary washer size from bolt diameter, clearance-hole size, application and desired load distribution.
The washer inside diameter needs to provide clearance around the bolt while remaining appropriate for the selected fastener system.
For a preliminary selection, the calculator uses the larger of the bolt-hole requirement and a small clearance allowance.
The washer outside diameter determines how widely the clamping force is distributed over the supporting surface.
Larger outside diameter washers generally distribute load over a larger area. This can be particularly useful for thin, soft or damaged supporting materials, subject to engineering verification.
| Application | Typical Selection Approach | Primary Consideration |
|---|---|---|
| General bolted joint | Standard washer proportions | Basic load distribution |
| Structural / heavy load | Heavier washer proportions | Bearing and strength |
| Thin material | Larger outside diameter | Load spreading |
| Soft material | Large bearing surface | Local crushing |
| Oversized hole | Large OD / special washer | Hole coverage |
The calculator first establishes the required washer inside diameter from the clearance-hole requirement. It then increases the outside diameter according to the application and load level.
A preliminary washer thickness is also estimated from bolt diameter, supporting material thickness and the selected load level.
How do I select a washer size?
Start with the bolt and clearance-hole dimensions, then select an outside diameter and thickness suitable for the required load distribution and joint material.
Should the washer ID match the bolt diameter?
Not exactly. The washer hole normally provides clearance around the bolt, so the appropriate inside diameter is generally larger than the nominal bolt diameter.
Why would I use a larger washer?
A larger washer can spread the clamping force over a larger surface and may reduce local bearing or crushing in thin or softer materials.
What is a fender or large-OD washer?
It is a washer with a comparatively large outside diameter relative to its hole, commonly used when greater load distribution is desired.
Does this tool select an exact standard washer?
No. It provides preliminary dimensions. The final washer should be selected from the relevant dimensional and material standard.
Can this tool be used for structural connections?
It can provide preliminary sizing guidance, but structural connections require verification against the applicable design standard and specified washer requirements.