One-piece, machined aluminum block converts AR-15 lower receiver to 9mm. Compatible with all, Colt-type, 9mm upper receivers, the feed ramp is cut for reliable feeding with all types of ammo, including hollow point and frangible ball. Roller retention device holds block securely in receiver, prevents accidental release. Hardened steel ejector, feed ramp and bolt hold open give long service life; last-round-hold-open feature on bottom-loading model works when used with Colt magazines. Also works with modified UZI magazines but last-round-hold-open will not function. No receiver modification required. Top-Loading Block installs from the top of the lower receiver and Bottom-Loading Block installs from the bottom of the lower receiver. SPECS: Aluminum, black, matte finish.