ADVISORY: This traditional style of in-line valve, originally introduced in the late 1990's by AP Valves in the UK for their Inspiration rebreather, was low height in order to fit inside a tight space under its back cover. In-line valves are still widely seen today with a variety of different rebreathers, although we are not aware of any modern rebreather that requires the low height or the bumper. The short in-line valve can be a challenge to tighten or loosen on the cylinder neck inlet because there is no place to get solid contact with an ordinary open-end wrench and specific techniques are required to avoid damage. However, technicians who are unfamiliar with this particular design have been known to just hammer on the side of the DIN outlet to loosen or tighten the valve and cylinder. Such forceful impact can cause the outlet opening to become very slightly out-of-round (see photo of an extreme example) such that DIN fittings will no longer screw in fully and properly seat. If you do not actually require the traditional version (and you probably do not), instead we recommend our DGX Gears Premium In-line Valves because they are a little bit taller in order to provide a proper wrench flat for easy installation and removal.