REV Building System also comes in a 15mm x 30mm square extrusion. The slots are designed to fit standard M3 hardware rather than expensive t-nuts. Use the 15mm x 30mm extrusion when more strength is needed for an application.
All holes can be tapped with an M3 tap.
Slots are compatible with standard M3 hex nuts and M3 hex-head cap screws as studs.