This is just a simple gantry design I made up to mirror the berrybot magarms as inspired by Xnaron's magnarms for the Rostock. Please note this is designed as a carriage to be used with Makerslide. I may produce a parametric version in future if required.
The two holes in the middle are for two m3 bolts to hold open ended MXL Belt. You will probably require a washer to hold them on and two cable ties to secure the loop back against itself.
There is also a dxf file marked 'cncable' which is a version you can have cut and then bend the top arms like on the berrybot to 90 degrees. I will eventually be upgrading to this so will update it when I get there if it needs any tweaks.