I bought a standard 21" light bar with factory brackets. I want to install the light on my grab rail above CC w/s. My brackets are the "half moon shaped" tilt brackets that mount underneath the light housing...not the ones with the 3/8" bolts. If you have a light bar attached to your railing with the type of bracket I have, can u post a pic. I haven't measured the railing really...pretty sure it's 7/8" OD. I wish I knew how to post pics, then I could show you what I have.
I have seen mounts that may work, but the fact is, they look like they may not Grip to the railing. I'd hate to drill holes in my railing.If you know where I can get some, chime in please. thanx

Go get some electrical ground clamps from Home Depot.

I looked at that bronze clamp. It fits 1/2"-1" materials..that's fine but I fail to see how I will mount that "under the light bracket". Will that screw hole at the top of that clamp accommodate a 1/4" bolt ?

It has worked for all of my rod holders, 42" light bar, bait cutting board, and everything else that I have mounted to the rail. I have yet to have had to drill out the hole for a larger bolt, but that is always an option.

Yes, it has 1/4 x 20 threads