Bushes are generally provided in a jig to

Explanation:

Jigs and fixtures are the auxiliary devices used in mass production. The fixture locates the workpiece and jig along with location, guides the tool. Jigs are used in drilling, boring, reaming, etc. and fixtures are used in milling, shaping, etc.

If deep holes are to be made in the workpiece, the drill acts as like a cantilever with point load (cutting forces). The hole becomes oversize in the beginning. Providing carbon bush makes it simply supported beam and hence the drill does not get deflected.

Hence the purpose of the bush is to guide the tool.