KZ305 rubber plugs impossible to find

Injected wrote:

If you want to reproduce that plug out of rubber on a lathe consider grinding it with rough paper or use a Dremel tool with a carbide burr at a fairly high speed (work piece one direction, tool in the opposite direction) Cutting rubber with conventional lathe tools only deforms it, the stuff is like chewing gum even at a high hardness.

I use to work for a rubber company doing prototype engine mounts, ground and carved a lot of different parts using all types of tools. Grinding it will give you a smooth uniform shape.