This is the 10 pack of replacement carbide inserts for the following part numbers: P/N 2253 80° RH Carbide Tool Holder, P/N 2254 80° LH Carbide Tool Holder, P/N 2255 Set of both 80° RH and LH holders, P/N 2264 80° LH 3/8″ Boring Bar w/Carbide Insert. Though not inexpensive, when you consider you are getting four cutting tools in one and are saving a lot of time in tool sharpening, it is really a pretty good deal. Carbide cutters give good finishes on hard-to-machine materials such as cold rolled steel. They will also work on aluminum, brass or leaded steels, and will last practically forever, however, the best finishes on those materials are still achieved with a good, sharp high-speed steel tool.