I knew for the first time a spring washer for stainless steel cap bolts. From the original, locking bolt does not protrude from the head width of the cap bolt and looks neater. It is recommended to those who stick.
The outline is just right, but I think it would be nice if there are several kinds of thicknesses, as is a special size flat washer
If there is 1 mm or 0.5 mm, the protrusion of the head portion of the low head cap bolt can be reduced