Because we located in the United States , we do not sell SCUBA cylinder valves with the metric M25 inlet thread form. We only sell SCUBA valves for use with US DOT cylinders, which all have imperial neck thread forms and are required to incorporate an over pressure relief device not found on M25 valves.

The ISO3601 standard specification of the o-ring for the metric M25 scuba valve inlet threads is a slightly smaller (25mm) inside diameter, and a slightly smaller (3mm) cross section than the AS568 standard specification for the o-ring of the imperial 0.750-14 NPSM scuba valve inlet threads, which is 1 inch (25.4mm) inside diameter and 1/8 inch (3.175mm) cross section. However, the AS568-214 imperial o-ring is close enough in size to the M3.0X25.0 metric o-ring that most divers consider the imperial #214 o-ring a suitable substitute.

One important safety caution regarding thread compatibility: The 0.750-14 NPSM threads most commonly seen on SCUBA cylinders in the US and M25 threads most commonly seen outside the US (particularly European Union) are very similar but not identical; with the use of force it's possible to mate diving cylinders and valves with these two different forms. However, the mismatched threads eventually separate with dangerously explosive force, often causing injury.