A4 (316 marine grade) stainless steel.

Stop that vibration working your bolts loose - a spring washer under that nut prevents your fittings flying over the side.

With washers we use the same size to suit both metric and imperial bolts.

Thus :

4mm washer will also suit a 5/32" bolt or machine screw

5mm washer will also suit a 3/16" bolt or machine screw

6mm washer will also suit a 1/4" bolt or machine screw

8mm washer will also suit a 5/16" bolt or machine screw

10mm washer will also suit a 3/8" bolt or machine screw

12mm washer will also suit a 1/2" bolt or machine screw

16mm washer will also suit a 5/8" bolt or machine screw

20% DISCOUNT WHEN PURCHASING IN BAGS OF 100.