Kris
I use in all my .21 motors a OD 287 plug.
It’s a variety of OS outboard , OPS DAC outboard, CMB Beta, Novarossi and even Picco P5 . All my motors like this plug .
Just FYI
Alex
Chris
After the print I sanded the surface with 400 grid paper.
Holds really really good .
Here is a list for PETG resistant.
http://kmac-plastics.net/data/chemical/petg-chemical.htm
Alex