woodcraft › Jet pen kit - Gun Polish Image 1 of 1 Jet pen kit - Gun Polish $29.50 This pen kit needs bushing for jet and a drill bit size of 9.5mm or ⅜ to bore for brass tubing. Add To Cart Added! This pen kit needs bushing for jet and a drill bit size of 9.5mm or ⅜ to bore for brass tubing.