For smaller applications the REV Building System also comes in a 15mm x 15mm square extrusion. The slots are designed to fit standard M3 hardware rather than expensive t-nuts.
This product is a 4-pack of 420mm pieces of extrusion, an appropriate length to fit within the frame perimeter on your FTC legal robot without extra cutting.
NOTE: we make two different size extrusions and the plates and brackets for each one are not directly compatible. Please be sure that you are buying the right bracket for the correct system when purchasing. The systems will either be marked 15mm or 1 inch.