From the horses mouth:
37-51 ALL
52-54 3/4, 1 TON, UTIL......VENTILATOR, rear axle (thread type)....3684539 .18c
52 PASS., 1/2 TON
53-54 ALL (except PASS., 1/2 TON)......VENTILATOR, rear axle (drive type)....3700490 .18c

So I guess your '51, 3104 should be a thread type, if it's stock that is.
Denny Graham
Sandwich, IL





Denny G
Sandwich, IL