Sometimes people in different parts of a technical community have regional connotations of technical phrases and names. We hope to address this in the Frequently Asked Questions detailed below:
The Term “ID” refers to Inside Diameter. Sometimes referred to as “Slip Fit“. The external diameter of the drill bushing is consistent for all the drill bushings in an ID Drill Bushing Set. However, the internal bore diameter varies being designed to correspond to standard, oversize or undersized aircraft fastener holes. Hence, the bushing is machined to accommodate a specific drill sizes. Note the machined receptacle in the external diameter . This is to mate with the set screw in the SAS Drill Bushing Block.
The Term “OD” refers to Outside Diameter. These bushings are sometimes referred to as “Transfer Bushings“. The internal bore of the drill bushing is consistent size for all the bushings in an OD Drill Bushing Set. Bushings with an OD of 0.1875″ or less have an internal bore corresponding to a #40 Drill (0.0980″). OD sized above 0.1875″ employ a #30 drill.
The outside diameter is designed and turned (machined) to correspond to the hole requirements for standard, oversize or undersized aircraft fastener holes.
Typically, this type of drill bushing is used in transferring fastener hole patterns. The process consists of using the OD Drill Bushing with an OD that fits tightly on the original fastener hole in the old component, and drilling a smaller “pilot hole” through the bushing into the new component.
Using an OD drill bushing ensures the pilot hole will be concentric with the original fastener hole. Furthermore, it ensures the pilot drill is maintained at 90⁰ to the surface being drilled.
In a separate step, the pilot hole is then enlarged to the final desired size.