Are you using a Rail plate 3/8 Inch? Please help.

Can the standard camera mounting knob be used to mount the Rail plate 3/8 Inch or is a knob with a shorter shaft required?
My camerma mounting knob will not screw into the brass part of the 3/8 plate. Anything more than 1 turn causes a jam requiring a pair of pliers to remove the brass part from the shaft of the camera mounting knob. I tried screwing the camera mounting knob into the shallow hole on the underside of the 3/8 rail plate, the fit was very tight and ultimately the shaft of the camera mounting knob is too long.

In conclusion there are three possibilities:
1. The standard camera mounting knob should fit into the brass part of the 3/8 rail plate and my older mounting knob is oversized or has a slightly different thread.
2. The standard camera mounting knob should fit into the brass part of the 3/8 rail plate and it is the brass part at fault.
3. The standard camera mounting knob is not meant to fit the 3/8 rail plate and a shorter knob is needed.

Regards,