Which thread is this? Measure the diameter over the crests and the pitch with a calliper, say whether it is male or female, and the page lists the matching threads used on regulator ports, hose ends, cylinder necks and valve connections.
Some threads share nearly the same pitch and diameter and differ only in their shape, which a calliper can’t see. The page flags these lookalikes, so you know when to check the marking on the part or reach for a thread gauge.