Ok I ordered
Davies Thermoplastic Four Arm knob, Flute Rim, Threaded Through Hole, 3/8"-16 Thread Size X 1/2" Thread Length, 2-1/4" Diameter (Pack of 10)
from Amazon $14.90. Got some flange nuts and 2 1/2" bolts at Ace Hardware. Tighten the jack clamps using the flange nuts upside down. See...