Anti-Vacuum Valve Stainless Steel 1/4 BSP This Stainless Steel is the "Upgraded" version of what is considered the most common anti-vacuum valve that is is present on many brands and models espresso machines. Although 1/4BSP is the most common size there are other sizes options, so please check the size of yours before ordering. The threaded area diameter is 1/4 BSP (is the equivalent of 13mm and approx.. 1/32"). A gasket is recommended for installation. NOTE: The lower portion of the plunger is taller compared to the older brass version, check the width of the fitting (IF mounted on a fitting and not directly on the boiler) If the fitting is smaller in ID consider this one instead.