The BOSTITCH BTMT72278 1/2" Locking Extension Bar Set The BOSTITCH BTMT72277 3/8" Locking Extension Bar Set is constructed of chrome vanadium steel for increased strength & durability. The locking component on these bars provide security for sockets on the extension to help prevent dropped sockets in engine compartments. Featuring anti-slip rings on the sockets which allow for easy gripping. This set features common extension sizes which are used for many typical applications.