Machined aluminum gauges give a precise, repeatable indexing reference so front and rear sights can be aligned perfectly, every time. Front gauge attaches to the gas cylinder (M1) or flash suppressor (M1A); rear gauge fits in the stripped rear sight housing.
Big Book Catalog, Issue:65, Page:478
Law Enforcement / Police Store, Issue:05, Page:048
SPECS: Machined aluminum, silver, matte finish. 6" (15cm) long, 1" (2.5cm) square. Includes illustrated instructions.