From G3 of Connecticut here in the USA comes a necessary tool for rimfire accuracy.
G3 Rim Thickness Gauge!
This tool is a must for sorting ammunition by rim thickness. Quickly and easily check the rim thickness. The tool attaches to your calipers. Absolutely the best way to sort. Reduces the variables that ultimately influence accuracy. Comes with a neck lanyard attached. No way to drop the tool and have an accidental rim hit. Will measure rim thickness on .22 Short, .22 Long Rifle..22 Magnum RF and .17 HRM