Injector pump O-ring size?

[Broomhall88]

Hi all, i have a leak from my injector pump and my friend fixing it is confident its the head seal o-ring.

he wants to know the size of the o-ring but i cant seem to find it anywhere on the net :( does anyone know?

Im guessing its the greenish 0-ring in the bottom left of this pic

TDI injection pump seal kit for leaking TDI injection pump (http://www.dieselgeek.com/TDI_Injection_Pump_Seal_Kit_p/pmp-fullkit.htm)

Thanks