Is there any marking or something obvious that I can use to identify the thread type on my kit?
Measuring the number of threads per inch (or mm) and comparing against a standard table is one way, but I had to do this at work one time and found that the simplest way is to hold up the thread to the light side-on so that you can see the peaks and troughs of the thread. BSP has a rounded peak(and trough) whereas NPT is more angular and has a flat section at the top of the peak so doesn't come to a point. This is why even when some sizes with the same number of threads per inch (1/2in, if I remember correctly) don't fit together for more than a turn or two - the shapes don't mesh together that well.
Was hoping it would be a stamp on the fitting or something.
Ive a mix of both all over my setup. PTFE tape & they fit nicely. No issues. I think there is only half a thread in the difference (WillD posted that a while back)
The 1/2 inch size pretty much interchangeable as the thread count per inch is the same -14 from memory. Other sizes become tricky and could lead to leaks or thread damage. +1 on ptfe tape
Ive only ever used half inch. Never even thought of the other sizes. Good to know.
Both 1 /2" and 3/4" are 14 tpi.
There is a slight difference in diameter due to the different thread angles: 55 degrees for bsp and 60 degrees for NPT. However the taper of the fitting allows them to fit together. Of the two combinations: Male BSP Femal NPT and Male NPT into Femal BSP, One is tighter than the other. Always use teflon tape!
For the techies:
NPT versus Bsp:
Npt:
Series Nominal Size Pitch Tpi Pich in " & mm
1⁄16 0.3125 in (7.94 mm) 27 0.03704 in (0.94082 mm)
1⁄8 0.405 in (10.29 mm) 27 0.03704 in (0.94082 mm)
1⁄4 0.540 in (13.72 mm) 18 0.05556 in (1.41122 mm)
3⁄8 0.675 in (17.15 mm) 18 0.05556 in (1.41122 mm)
1⁄2 0.840 in (21.34 mm) 14 0.07143 in (1.81432 mm)
3⁄4 1.050 in (26.67 mm) 14 0.07143 in (1.81432 mm)
Bsp:
Series Nominal Size Major Dia in Major Dia mm Pitch tpi Pitch mm
BS Pipe G 1/16 0.30400 7.72160 28 0.9071
BS Pipe G 1/8 0.38300 9.72820 28 0.9071
BS Pipe G 1/4 0.51800 13.15720 19 1.3368
BS Pipe G 3/8 0.65600 16.66240 19 1.3368
BS Pipe G 1/2 0.82500 20.95500 14 1.8143
BS Pipe G 3/4 1.04100 26.44140 14 1.8143
Good to know that 1/2" works for a brew, but I can guarantee you it doesn't seal at higher pressures! You can buy thread gauges on line that measure the thread, the cheap ones are just a set of 'keys' with the thread profiles outlined on them, they're only a few euro (or used to be anyway). However, if you're dealing with 1/2" where the threads per inch is the same, visually checking the profile is the best way - try it, it's easy enough, particularly if you have both types to compare against each other. And it will be a great new trick to impress your friends down the pub!