This is the 'beam' part of 'Open Beam', the central building component for the system.
Wow. The OpenBeam Kickstarter really pulled through, and ...it's nice stuff! We invested in the MakerBeam stuff a while back, and it's been great for some tinkering, but this OpenBeam really pours on the utility-sauce!
Designed around metric hardware standards (yeah, seems metric is the way to go with this stuff!), the OpenBeam 1515 extrusion features 4 slots that perfectly capture a M3 hex nut or the head of a M3 hex head cap screw.
The center hole channel in the beam can also be tapped to accept an M3 screw, for nifty end-mounting applications The channels down each side of the beam are 3mm wide, handy for 3mm acrylic, 1/8" wood. Thinner material like (interestingly enough) standard 0.062" circuit-boards fit nicely into the single thin channel that runs down the center spine. It's a really well thought-out profile, which is sure to see lots of applications in the DIY machine field!
OThese extrusions are precut to 30x15x15mm (LxWxH)