Black Diamond
Airlock Screwgate (1997) (recessed seat) (green sleeve)

A compact S-Spine belay carabiner that BD designed for use with the ATC belay device. Hot forged, with large rounded surfaces and distinctive large lettering along the trapeziodal spine. Only marked for Major and Open gate strength ratings, the catalog listed (the relatively low) 6kN as the minor axis strength.

Despite using a snap ring upper sleeve stop as found on later model BD carabiners, the sleeve jams against the nose at full lock.

The tapered diameter locking sleeve indicates a 1997 (or later) model year, as Black Diamond 1997 Spring catalog shows tapered sleeves (along with the release of the mini-pearabiner), whereas the 1996 Spring catalog still shows uniform diameter full length knurling on locking sleeves.

The 1996 uniform width sleeve version lacks batch marking of any kind.

Of the tapered sleeve Airlock carabiners, I have two slightly different locking sleeves:

The red sleeve example has a flat bottomed locking sleeve, which rests directly against the lower sleeve stop ring. The green sleeve example has a small recess turned along the interior bottom of the locking sleeve, allowing it to partially cover the lower sleeve stop ring.

The sleeves also have different unlock rotations and maximum rotation distances, but it's unclear if this was a design change or could be attributable merely to manufacturing variance or wear.

If the red sleeve was not formed in error, I would guess that the green sleeve was produced later, as later models of BD tapered sleeves have this recess. Both examples have the same finished batch marking, so this would have been from the sleeve production.

The Airlock had a relatively short production run, and climbers tended to only buy a couple, making it not as common as other 1990's BD carabiners.

The much longer lived Airlock2 carried on the Airlock name for many years.