/diy/ - Do It Yourself

Hey /DIY/

Im trying to build my own sex machine (pic relate). Ive gathered most of the materials required but im having trouble finding a fitting to use as a "channel" or "bracket" to stop the plunger from going in all directions.
I know theres plenty of metal hooks i could use but im looking for something to prevent metal on metal reciprocation.
The closest thing ive found on google images is a "plunger" or "piston" buffer .
It doesnt need to be air tight however just not metal.
Im not even trolling, could someone please help point me in the right direction .