If my memory serves me correctly they're 1/2" by 20 thread pitch. They are available through Cat still, I'm away from my books right now so I can't give you a part number. I've bought them from Florin Tractor also, those are aftermarket but are basically the same.
Clutch Handles are part No. 0L0829 and Gear Stick Handle is 0L1170 Both Readily available from Your Cat Dealer . LJ
Regal has the steering clutch handles 0L0829 @ $6.40 each.
The 0L1170 @ $5.69 ea.