Crystal chamber with 1.14in OD, Part 2 - Brass insert.
(or you can also choose 2 x Part3 instead)
For MHS extension, and can be used with Double male with slots style 2 (the design matches the slots on this extension).
Check this post:
http://goth-3designs.com/instructions/diy-crystal-chambers/
Depending on the material used and due to the printing process accuracy, parts might need a bit of sanding here and there to fit properly.