A 3/16 x 1 1/2" solid pin is recommended. A spring pin of the same size will probably be adequate. The pin does not bear weight from the patient. It assists the locking handle in keeping the lock engaged in the rotation casting.
Drill and pin at this location. Drill deep enough so that the hole in the rotation casting is about 3/4" deep.
NOTE: This only needs to be done if the gussets are not present on the crossbar collar.