Tool for measuring the inner and outer diameter of refrigeration and air conditioning capillaries, instrument for measuring the inner and outer diameter of copper tube capillaries

While imperial sizes have been adopted as the norm in the world of plumbing, with BSP as standard, it is not uncommon to find the odd metric thread size. But what do figures like 15/21, 1/2, DN20, 12/17 mean when it comes to plumbing fittings? Read on for all you need to know about plumbing thread sizes.