From what I understand, a liner locates removable pins etc. in the fixture to hold assemblies in the correct location. In my application, it has to be a close tolerance wear resistant bushing to improve life of the fixture. The drill bushing guides the drill in the machining operation. The bushing diameter must be close tolerance to keep the drill from drifting and creating a hole out of location and also must be wear resistant. They both seem to be close tolerance wear resistant bushings which makes me confused as their possible interchangability