Bencher--Majestic Tripod Head question

I've just purchased an old Majestic tripod head that doesn't have a model number on it but it looks very much like a 1200. Does anyone know how/if it's possible to remove the stud adapter that screws into the bottom of the camera? This one came with a 3/8" size and I want to use a smaller one but I can't see how to remove the spring loaded collar around the thread.

Thanks.

Allen screw--teeny tiny one--in the knob you turn to tighten the thread--take out the allen screw--there are TWO of them usually--one comes out and another one deeper inside--then twist off the knob and the whole collar/spring stud will come apart.

there are 1/4 and 3/8 studs/knob/collar asseemblies--it's easiest to get one than to make one.

That's great. Many thanks