This is an osVAC M32 adapter for the 12 Gallon Shopvac vacuum. It repurposes the original Shopvac screw on adapter that is attached to the original small hose to attach this adapter. See images for more details.
Instructions
Unscrew original small diameter hose and its adapter from the inlet.
Pull off the hose from the inlet adapter.
There will be a screw ring that freely rotates around the adapter. Start to pull it off by hand. If you're unable to, use channel locks on their largest setting and put the bottom jaw on the bottom of the adapter tube and the top jaw on the top of the screw ring. Work the channel locks around the ring as you slowly guide the screw ring off the adapter.
Put the screw ring on the new osVAC adapter and again use channel locks to move the screw ring up the adapter.
After the screw ring is in place, screw on the new adapter to the Shopvac threads!