Cable Gland and Low Voltage Control Cable 0.6/1 kV

You will have to know the outside diameter of each cable. The gland manufacturer lists the minimum/maximum diameters each will hold. You first pick one you think you can drill a hole for, if box mounting. (that becomes a real problem in the USA when trying to decide which metric diameter is closest to a bit sized in fractional inches that is in stock in your machine shop) Then check the range of cable diameters the gland will fit. (look at the min listing and the max lsting - is your cable within this range?) If the gland fits use it. If not, go to a bigger or smaller one, whichever is required. No magic here - no rules or regulations - just some common sense.

By the way. As I am told, the PG gland sizes are becoming obsolete and the simple metric sized ones are the ones to choose. We use NPT here in the States, which probably should be obsolete by now, but we just can't change our ways.