EXTSW 5/16” ID x 1 3/8” OD x 1/4” thick 304 alloy stainless washers
Actual size .323 ID x 1.365” OD x .250' thick
(+/- .003" on all dimensions) 
.030 inch Radius OD / slightly countersunk ID (no sharp edges)
 Made in USA. 304 Stainless has the very GOOD corrosion resistance.