@futurebird the ones that are hard to find in home improvement centers are those designed for tracks. Like t-slot or mitter nuts (used in tools like circular saws, routers etc to screw hold down bolts. Or hammer nuts for fastening to extruded aluminum frames after the frame is built (can be used with tracks too)
@Altreus@futurebird depending on the clamps you use, a low profile head bolt can be used in a t track and with a wing nut or knob nut, makes for a greater range of adjustments.