After chasing seals for my Futura "Brembo" Master cylinder I can confirm the following part numbers.

The actual dimensions of the Master piston/bore it is to fit is 12mm od x 7mm id x 4mm SU12-7-4-EP-DS106 IS CORRECT


The actual dimensions of the Master piston/bore it is to fit is 12mm od x 5mm id x 4mm SU12-5-4-EP-DS106 IS CORRECT

The actual dimensions of the Slave piston/bore it is to fit is 28mm od x 20mm id x 4mm wide SU28-20-4-EPDM-DS106 IS CORRECT

The suppler is FPE Seals Ltd, 7 Barrington Way, Darlington, County Durham, DL1 4WF, England.

The staff are extremely helpful.