As an ex-brat F2E and an Ex- Shack driver I really should remember.
The CSU was mounted on the rear prop and controlled it directly, then as Virgo says from that there were three "rack bolts" which each connected to it's own front blade and turned the blade so that the pitch of each front blade was the same as each rear one. A system that sounds a bit Heath Robinson but worked!!. Trouble came if you had a rack bolt failure, its connected prop would normally fine off to the feather position whilst the other five blades continued to obey the CSU much to the distress of the poor old Griffin that it was connected to and the airframe as well. It was however robust as in x'000s of hours in the old Grey Lady it only happened to me once.