Tie-rods are the ideal attachment mechanism in that it forces the designer to only load joints in the proper way. They eliminate torsion loads and any bending moments. Working in aerospace we see this type of support very often. Rod-ends come in male and female, right- and left-hand thread. Male rod-ends are used to screw into hex or other tubing with inside threads. Female rod-ends are more common in small sizes and are used with threaded rods.
In order for them to work with Microrax support structures, we need to find rod-ends with a ball bore of 3.0 or 3.1mm. That allows us to use 3mm shafts that fit right into standard Microrax parts (plates). Ideally the ball width (widest part of the rod-end usually) be either just under 10mm (to fit the standard Microrax profiles) or else use small washers to space the tie-rod centrally between the two support plates. This is called a Clevis joint and in engineering is referred two as double-shear (the best kind of joint joining two parts since it is symmetric). In Figure 1 below you the top joint is in single shear (since the force lines do not line up they will create an unbalanced bending moment on the bolt and the plates) and the bottom joint is in double shear.
RC4WD (http://store.rc4wd.com/) manufactures many rod-ends suitable for prototyping in small sizes. For example they sell M3 Aluminium/Steel ball rod ends for under 3$ (about a third or less of the price McMaster charges!).
You can buy through the RC4WD page other RC companies (eg:http://www.rcrockcrawling.com/index.php?cPath=51), for the same price.