Just a quick slide in T-Nut thing i made up for some Slat Wall. I saw another out there with just a hole in it for use with a wood screw, but this will accept 1/4-20 nut or bolt, and is meant to be able to slide around and then tightened down. (Ill use it for a clamping board for my CNC router)

Could this be turned into a drop in type (for those who have this stuff on a wall? Sure. But a 1/4-20 nut/bolt would not work.

Step and solidworks (2014) part included so you can change bolt sizes if you want. The nut/head hole is slightly tapered on 2 sides, not sure if it really does anything, but I added it anyway. If you adjust it to a different size, you can probably just skip out on this, as its so small (like .025mm).
If i ever figure out how openscad works, ill maybe redo it so you can just enter the size of bolt/whatever that you want.