I'm about to fit a new Hudson Reed Triple Control Thermostatic Shower
Valve.

In the instructions, in the section about connecting to water supply
it says :

"Connect the hot and cold water supply feeds to the shower valve,
using a suitable brass parallel thread male iron and swivel
connector".

It has a similar phrase about the connection to the shower outlets.

I thought I knew what a male iron was but I'm not sure about the
swivel connector. Does anybody know exactly what I need and if I can
get them from screwfix or will I have to got to a specialist Plumbers
Merchant? Why does it need a swivel connector?

I'm not actually sure what size the connector is and there's nothing
on the instructions to indicate this. It's at least 22mm but is it
more likely to be 1inch? By the way I'll be connecting it to 15mm
copper for all inlets and outlets.

Thanks