Does anyone know what pipe thread standard is used for the input water supply line on the direct connect Vibiemme espresso machines? The hose terminates in a male threaded fitting. How about the Inoxdep rechargable water filter that is sold by 1st-line? It has a male fitting for input and output. Both items are manufactured in Italy, so unless it was specifically modified for the US market, I imagine it's whatever is normally used in Italy.

I called 1st-Line tech support today and was told that they were "metric threads". I found a metric thread standard ISO 261, but that seems to describe screw threads rather than pipe threads, as best I can tell. Home Depot and Lowes and similar stores only seem to carry NPT fittings. I know I can get most anything that is made from McMaster Carr. I don't want to use the wrong type of fittings and risk damaging the existing threaded fittings.

1st-Line has a 1.5 meter hose with female couplings on both sides and a female/male adapter that I can use to extend the water line on the VBM and connect to the output side of the water softener. But I still need to know the pipe thread standard, at least for the water softener, so I can connect the input line to it (output from my sediment and charcoal filter).

They are BSPP threads in accordance with ISO 228. I BELIEVE the male thread on the machine is 3/8"-19 BSPP. If so, it would have a diameter of ~16.7 mm. The fittings on the water softener you referenced are similar, if not identical.

BSPP threads are oftentimes referred to as "metric" but that is incorrect.

Thank you Eric. I know that the big box home improvement stores don't carry such fittings, but there are several plumbing supply stores around here where I think I'll have better luck.

There are two types, BSPP and BSPT. The P is parallel thread the T is for taper thread. Parallel thread seals against the back of the fitting it is screwing into. Taper thread seals against the threads. McMaster-Carr carries a lot of fittings and adapters for BSP to NPT applications.

That's good info, Dave. Eric said that these are BSPP in this case, so hopefully I won't find out they are BSPT. I'd hate to have to buy parts twice!

I believe the machine fittings and hose ends are all parallel-threaded (ISO/BSP); I don't know whether the inoxdep fittings are parallel or tapered. Here's a reference to some adapters that may be relevant:
http://www.swagelok.com/search/find_pro ... b802a7f8ac