princess disc dimensions

mick

south shields

just a quick techy question. im building a hybrid mini. and after some basic info from a guy who used to do sprints and hill climbs he gave me some brake info. i am using a mini hub assembly a ldv 200 city van 4 piston caliper, and he told me to fit a princess disc which will be machined down to fit inside the caliper. what i need to know before i order some discs is what is the distance between the holes where the disc bolts to the drive flange. sizes in mm would be appreciated. thanks .