Factory Specified Size Measures M16/AR-15 Maximum Headspace
Made to the Colt factory's special dimensions for M16/AR-15 rifles.
It measures the maximum factory acceptable headspace; an
essential check on guns that have seen extensive service or have
AR-15, Issue:08, Page:070
AR-15, Issue:08, Page:074
Big Book Catalog, Issue:65, Page:068
Big Book Catalog, Issue:65, Page:072
Law Enforcement / Police Store, Issue:08, Page:054
SPECS: Hardened and ground steel. 1.65" (4.2cm) overall (this
is NOT the "headspace" dimension). .3655" (9.3mm) diameter.