Master cylinder help.

[jeffbcn]

47 chevy thriftmaster, stock brakes.
There is a threaded rod with a jam nut on it that comes out of the front of the master cylinder. Is this for pedal adjustment ? If so, how? I just had brakes adjusted and bled. Petal is about 3 to 4 inches from the floor. Drums and shoes good, new wheel cylinders. It that normal? The rod coming out of the master shows almost an inch of thread and the jam nut was loose.
Any help would be appreciated.