Auqalung/US Divers Arctic and Octo parts kits?

[AFdivedoc]

The arctic is a bit of an oddball reg when it comes to parts. You can download the manual from VDH as Umuntu noted above. The poppet nut is 5.5 mm (rather than 1/4"), and it requires a 5.5 mm nut driver to remove and to install/adjust it. Be warned, not every 5.5 mm nut driver will do the job--the socket wall may be too thick for the diameter of the recess of the nut. If you can't find a parts kit, McMaster has the right stainless steel lock nut for the job if yours needs replacing(size M3 McMaster-Carr ). The low pressure seat (rubber puck for unbalanced regs) is the same one used everywhere, and available at VDH.

I recently got one back up and running. Actually it was more straightforward than I thought it would be, and it breathes pretty well.