These bushings are intended to be used with gun-drilling machines. They are similar to Slip/Fixed renewable bushings, but with the drill bearing at the bushings head end. All American type GDB bushings are heat treated to RC 62-64 and ground concentric with .0002 T.I.R. The head is undercut and ground square to the O.D. within .0002 T.I.R. These bushings are considered as special and not returnable. Prices available upon request.