Chase & Clean Threads For More Accurate Installation
Chases and cleans the two most important threads on the AR-15/M16 receivers. 1.250"-18 tpi - Corrects out of spec or cross-threaded upper receivers and barrel nuts. 1-3/16"-16 tpi - Makes receiver extension (recoil buffer) tube and lower receiver threads uniform for easier installation.
AR-15, Issue:11, Page:086
Big Book Catalog, Issue:72, Page:091
SPECS: High-speed steel. Plug taps; 2½" (6.3cm)