This hardwood bar-clamp rack can be made as long as needed, with the spacing altered to hold every clamp in your shop. The rack features beefy mortise-and-tenon brackets and a tapered back plate that tilts the brackets up slightly to keep the clamps from sliding off.
To make the rack, start with a back plate that is 1-3⁄16 in. thick by 5-5⁄8 in. wide and as long as you want. Saw the back plate in two lengthwise, and use a dado blade in your tablesaw to notch in the mortises (space the mortises so that the brackets will fit your clamps; in my case 1-3⁄16 in. apart). Glue the two halves back together to form the throughmortises. Now taper the back plate by tacking a 1⁄8-in.-thick by 3⁄4-in.-wide strip along the face near the top edge. Run the back plate through the planer until the top edge is 1 in. thick and the bottom edge is 1-1⁄8 in. thick. After planing, remove the tacked-on strip.
I made the brackets that hold the clamps 1-3⁄4 in. square by 12-1⁄2 in. long with a 1-1⁄4-in.-square, 1-in.-long tenon on the end. Attach the rack to the wall with screws through the back plate into studs.