This Slip Fit ID Drill Bushing (Internal Diameter) is precision machined from O-1 Tool Steel.  Each piece is subsequently heat treated and tempered.  This results in an extremely hard tool which is almost impervious to wear from the drill and the drilling chips. 

The Outside Diameter (OD) of this model number of bushing is 0.501" (tolerance  ± 0.001”).  

Note the receptacle in the outside diameter, 1/2″ below the bottom of the bushing head.  This has been machine in the OD of the bushing to accept the anti-rotation set screw when used with an SAS-Canada Drill Block  and SAS-Canada Drill Cup.