15mm x 30mm Extrusion
The 15mm x 30mm profile of the Extrusion has slots on on all four sides that accept standard M3 hardware. Rather than using a T-nut, which is more expensive, slide a M3 hex head screw along the slot and adjust brackets and other build materials as needed. As illustrated in the image above, the ends of the Extrusion also have a 5mm hole pitch that can be M3 tappped. The 15mm x 30mm Extrusion has one slot on each 15mm face and 3 slots on each 30mm face, allowing for some additional design flexibility when compared to the standard 15mm extrusion.
The 15mm x 30mm Extrusion is great for areas where more torsional strength is needed in an application than the standard 15mm Extrusion.
The point of the extrusion system is to offer more flexibility in design than would come in a fixed pitch system. The slots in the extrusion allow brackets and other components to be slid along the 15mm Extrusion to an infinite number of positions.