1. Browse to Kohler K-29709-CP (I assume this is your model)
2. Expand Installation & Service Parts
3. Click 'Service Parts Diagram'
4. Note that the handle is tightened by Part number 1059613 which is covered by Part Number 1219282

Thanks. yes, that’s the faucet and the exploded view shows the parts I’m seeing. But the nut doesn’t appear to have threads on the inside, and I can’t see how it stays on. I loosened it, thinking it had threads, but didn’t take the lever off. Now it is just pushed on over the o-ring, and doesn’t tighten when turned. I didn’t remove the lever handle, so it wasn’t completely off the faucet, just not in place. May have to take it all the way apart to get a better look.

"But the nut doesn’t appear to have threads on the inside, and I can’t see how it stays on."

I presume that the nut just presses on over the #43167 O-ring and the M4x25 screw (part #1059613) holds the handle on.