Wow thanks guys, OK, so the left crown is a TC branded crown as far as I'm aware and the right crown is sterile which is why I want to change out. Both tubes fit the stem on both my GMT and Sub, but the crown on the left does not screw onto either case, both watches look to be Parnis I assume and I was hoping to mod.
GMT is a 166110 style and the movement no longer sets correctly. My skills are not there yet to fix so I thought I might try to mod my Sub instead, will add some pics but really appreciate the help thanks