The size of a plumber’s turnpin refers to the diameter of the broadest end.
Imagine a straight line passing from one side of the turnpin’s base to the other through its centre. This is the diameter and is a measure of how wide the base is.
A plumber’s turnpin typically comes in one of two sizes:
38mm (1.5 inches)
50mm (2 inches)
When choosing the size of the turnpin, make sure that it is large enough to expand the opening of the pipe.
The expanded pipe opening needs to be large enough to recieve the mating pipe.