Headspace Gauge 7x57 Mauser , and 257 Roberts Field Gage Precision Machined from hardened tool steel to last a lifetime of use. Must have Tool to check the chamber headspace. Headspace tolerance is ground to a very exacting  0.00015 in. Made in USA , ISO9001 Quality Standard For all 7x57 , 7mm Mauser chambers including surplus military and 257 Roberts.