They are the same as on the tailcap-end of the standard-body. I measured a thickness-diameter of 1,5mm. I don't know how to measure the diameter of the whole O-ring, but:
I measured an outside diameter of 15mm.
O-Ring at the head:
thickness 1,9-2mm
outside diameter 17mm.
O-ring at CR123-tube:
thickness 1,0-1,1mm
outside diameter ~10mm.
Dirk