Polytetrafluoroethylene, or Teflon, is most commonly used for gaskets, valves, rings, seals, and other similar applications. PTFE is softer and therefore not as easily-machined as PEEK or Delrin, but is one of three plastics we see most often.
Polyether ether ketone is a common plastic that is easily-machined and used for its insulating properties. We have made medical parts from PEEK.
The best machining plastic material, delrin is tough and used for gears and other industrial applications.