Radiator Valve Tails

Radiator valve tails make the connection between central heating radiator and valve.
There are two main types of tale :
Standard radiator valve tails have a 15mm compression connection for the valve and a 1/2 inch BSP male thread for the radiator.
Union radiator valve tails have a face to face connection for the valve with a 3/4 inch BSP female threaded loose nut and a 1/2 inch BSP male thread for the radiator.