This Reamer Stop is a collar that slips over the shank of a chamber reamer. It is then locked into place using the set screws. The Reamer Stop prevents cutting too deep. Fits and ECT chamber reamers. Technical Information OD: .850" Material: Steel Notes: A great tool designed to attach to the shaft of your reamer to assure you do not cut to deep. Attaches to the reamer with one allen head screw. (wrench not included) Fits 3/8" (9.5 mm) square drive shank reamers.