Which wheel cylinder?

[gumby6371]

i've got a small fluid leak on the rear drums so I'll be doing a cylinder and shoe change at the weekend, pricing them up on euro car parts they list 1 with and 1 without integrated regulator.
How can I tell which one I need?
Obviously I want to fit new ones ASAP so a prompt answer would be much appreciated.

Cheers

Gareth

[jasper5]

Usually the one with the built in regulator has a 13mm brake line nut with the other having a 10 or 11mm nut and is always more expensive.