How are washers identified and measured?

Washers are identified and measured differently to nearly every other fastener we stock. Let us explain.

When searching our website, you will see washer sizes begin with M5, M6 or M16 etc, the M means Metric and Imperial washers begin with 1/4", 5/16" and 5/8". This size indicates the size bolt it was made to work with. For example, if you need a washer for a M10 bolt then you need to look for washers that start off with M10. 

If you have a washer and you are unsure of the size, first measure the inside diameter (ID). Let's say it measures approx. 9.70mm. That means you most likely have a M10 washer. If the ID measured approx. 6.50mm then it is most likely a M6 washer.

The key is always measure the ID, then go to the washer category, use the menu filters to narrow your search, choose the closest size down from your measurement and then open the item, scroll down and cross check the sizing on our technical specifications table. 

On some washers you will see M6 (1/4") or M8 (5/16), this means they are interchangeable and can be used on either metric or imperial fasteners. There are some sizes where we do not list both, like M10 and 3/8" because a 3/8" washer won't fit over a M10 bolt and a m10 washer is too loose on a 3/8 bolt. 

A little Disclaimer: We find measurements for washers to have become very inconsistent, in particular, the ID and thickness regardless of who we source them from (we do not import our own washers). Over the years I am certain the min and max specifications for washers have widen. As a low-cost high volume item it seems importers do not pay the same attention to ensure it meets the standard like they would if it was a bolt or nut. We are constantly monitoring our washers and if identify washers that we regard to be well outside what we classified as "acceptable tolerance" we will remove them from sale.