single tank adaptor

Howdy! I've been trying to search for this item but I can't seem to guess what it might be called. There must be about half a million of them out there that nobody wants so it would be silly to try to make one. They were common in and around the 70s (maybe) and perhaps the 80s. They were...

I have 1 x ScubaPro and 1 x OMS single tank adaptor (STA) for sale. Make me an offer! Both in very good used condition, no damage, no stains and constructed from heavy-duty stainless steel. The ScubaPro one also comes with 2 x barely-used counter weight pockets, RRP $80.30. ScubaPro OMS...