1502-1 Threaded Shaft with 3/8-16-1A thread.  1A thread is a loose thread that allows for easier threading of the knob.

1502-1 is made from stainless steel and is used with the M15 vibratory machine. 

The 1502-1 shaft is used to secure the lid of the M15 bowl.

Looking for the knob that goes with the 1502-1?   Part number 1500 is your knob.