The Studica Robotics 288mm Flat Beam is 3mm thick and 8mm wide.

The Studica Robotics 288mm Low Profile U-Channel (2-pack) is 3mm thick and has a 48mm x 14mm profile. As with the other Studica Robotics building components, it has the common hole pattern which makes it easy to connect to other structure with very little or no additional machining required. You can easily connect to other channel, extrusions, bushings, bearing, mounting brackets and more so you can quickly assemble and disassemble robots and automated systems.

The Studica Robotics 288mm Square Beam is 8mm by 8mm. 

The Studica T-Slot Extrusion is available in 10 different lengths from 48mm to 1000mm. It is strong while light weight. It can be easily cut to your own custom size. It has a 14mm through hole that will fit the Studica 6mm ID x 14mm OD Flanged Bearing or Bronze Bushing. It uses the M3 T-Slot Nut Hammer Head Series 20.  It also has four M3 threaded holes on each end. Use it as structure on infinite applications.