Half inch or 3/4 inch shower attachment

[GeorgeEliot]

need to get a replacement shower head and the model we have got come sin either 1/2 or 3/4 inch, but no idea what that refers to so don't know which to order.

Please could someone with a modicum of plumbing knowledge enlighten me.

It's the diameter of the pipe that the shower head will screw into. You probably have 1/2". The figure refers to the inside diameter so if you measure the outside of the pipe it will be slightly over 1/2".

thank you!