Sorting ammo by rim thickness will provide ammo with similar ignition qualities for improved accuracy.
This proven technique is used by competitive shooters and varmint hunters.
The rimfire gauge attaches to your caliper and includes bushings for use with most .17 and .22 caliber rimfire ammo including LR, WMR, HMR.
Hornady recommends you wear the lanyard around your neck and attach it to your caliper to promote safety.
Note: Vernier caliper in photo not included