Whidden .22LR Headspace Gauge Set These headspace gauge sets will allow you to determine the headspace on your .22 LR firearm. Seven gauges are included to indicate headspace from .039a ^2 to .045a ^2 or from .046a ^2-.052a ^2. Each gauge is marked with its size. Use these to check existing firearms, when installing prefit barrels, or along with Shim Kits to fine-tune headspace to match your ammunition. Headspace gauges are made from stainless steel. The 3-D printed storage box is included.