Most espresso machine fittings are BSP, which are also referred to as "gas" fittings. They come in Imperial sizes (1/8, 1/4, 3/8...), not metric. The thread pitch is different from American NPT fittings and therefore are not interchangeable. BSP fittings come in two versions: BSPP (parallel / straight) and BSPT (tapered). In almost all cases, only BSPP threads are used in espresso machines.
Water Pressure Regulators, John Guest Fittings, Brass BSP (British Standard Pipe) Fittings, NPT (National Pipe Thread) Fittings, Thread Sealant, Copper Pipe Components, and more.