it can butt up against another object. Another option to keep the renewable bushing from rotating is to pin it, either by putting a pin in the renewable bushing and a hole in the liner or vice versa. A more complicated version uses a hole in the bushing collar and a pin with a head; the head on the pin holds the edge of the collar down, but for removal the bushing can be rotated so that the hole lines up with the pin. Specification Customary bushings are specified using the following specification layout: ID-Type-OD-Length Where the ID is specified as a decimal, drill letter size, drill number size, or fraction; the OD is an integer that relates to a multiple of a th of an inch (); the length is an integer that relates to a multiple of a th of an inch. The lengths of press-fit bushings are standardized to typical jig plate thicknesses: , , , , 1 , , and inch (, , , , , and ). The letter "U" is used after the OD number to designate that extra stock should be left on the OD for grinding to size. The type is a letter referring to the following: S - Slip renewable F - Fixed renewable L - Headless liner HL - Head liner P - Headless press-fit H - Head press-fit The following two tables give the tolerances for the ID and OD. Custom bushings A common problem encountered is when two or more holes are too close for independent standard bushings. In this case one large renewable bushing can be made with two (or more) holes in the proper location (the first example in the image). Another possibility is to make a custom bushing with an eccentric hole and then notches on the outside of the head are used to locate the proper position of the bushing for each location (the middle example in the image). Another common need for a custom bushing is when the hole needed is perpendicular jig plate; in this case a bracket bushing is used. It is a hardened piece of right angle steel that screws to the jig plate and is located with dowel pins. Design In general, a drill bushing's length should be at least 2 times the nominal ID. References Bibliography Metalworking tools