The sensor to flange spacing (backfocus) for Hypercam Fan Cooled Cameras is 12.5mm, as measured from the front foremost part of the flange excluding threads.
Both Hypercam Fan Cooled and TEC cameras have a front female T2 thread. The specification of T2 is M42x0.75mm and the thread depth is 4mm.
The distance from the front of the flange, excluding threads to the sensor (backfocus) is 12.5mm for Fan Cooled cameras, and 17.5mm for TEC Cooled cameras. To learn more about getting the right spacing for your reducer or flattener read this article about reducer flattener spacing.