Generally
An extra long nipple for 3/16″ brake pipes, this nipple fits brake pipes that have an outer diameter of 3/16″ = 4.8mm. The outer dimension of the nipple is 3/8″ approx: 9.5mm if you measure with a caliper. Check the dimensions carefully, it is not always the same dimensions on all nipples for a brake system. The threaded part of the nipple is 16mm