Thanks guys. I bought some of the brass ones at Ace. The problem was that they weren't long enough to be used for my Trapdude soft top's against the adjustment pins. When they're originally made they just thread the plastic base. Once the threads wear out the inserts work nice, with allen screws, but I can't find any that are long enough.
Unless the thread is very close to the top or bottom of the plastic, they can be drilled out and re-threaded for a larger set screw.
If you try putting any sort of threaded insert in there, and you don't drill and tap the hole first for the thread that corresponds to the insert, you WILL split the plastic base and ruin the comb, no doubt about it. The gun nutz and similar inserts have a WOOD SCREW thread, which you won't be able to tap for, so you need an insert with MACHINE SCREW threads, which you can drill and tap for.
THIS is what you want, assuming there is enough room to re-drill and tap for a 5/16-18 thread. http://www.mcmaster.com/#90259a129/=qgyhpv
Don't worry about the overall length, just put some permanent loctite or two part epoxy on it, and thread the insert in until it just clears the post. Then when it sets up, you can screw your set screw into it. The one @ the link I posted will take a 10-32 set screw.
Another alternative depending on how far you have the comb raised would be to make a 3/8" to 1/2" aluminum bar, screw that to the comb, then drill and tap the bar for set screws.