Check the listing for details. GRAINGER APPROVED SFT568MM Drill Bushing,Type SF,Drill Size 21/32 11R578. Condition: New. Listed at 16.04 USD. Slip-Fixed/Renewable Drill Bushing (SF), Thin Wall, Headed, Fractional Inch, 21/32 in These slip-fixed/renewable (SF) drill bushings come in standard sizes expressed in fractional inches. Thin-wall slip-fixed drill bushings save space and can be placed closer together than standard-wall slip-fixed drill bushings.Slip-fixed/renewable (SF) drill bushings, also known as removable drill bushings, can be removed and replaced when worn. They are ideal for applications where bushings need to be changed between tasks or where bushings are expected to wear out before the job is done. Drill bushings are installed into a drilling jig to guide, support, and position a drill or other cutting tool during metalworking tasks. They keep the cutting tool from wandering or bending as it enters the workpiece,.