Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2157734.
This is a redesigned backplate for the rigid header with integrated beltlocks for GT2 belts. Just put the belt through the slit, insert the lock and pull a bit : locked. push the belt and the lock unlocks. No issues with getting the belt through the holes and locking them with tiewraps. The backplate will be even more rigid since the holes for the belt are gone.
Those who want to use the locks for their own design : the locks have an angle of 17,1°. I suppose you can neglect the 0.1°
Printing I printed the backplate with a 0,6mm nozzle in ABS, 0,4mm layer for the part up to the beltlocks, from then on 0,2mm layers (due to the details of the beltlock). Infill 60% full honeycomb. Do check the support generated by your slicer (see picture). I included the factory file for S3D users. The locking parts were made with a 0,4mm nozzle to get good teeth to hold the belt.
Testing This combination has been tested and found good for use.The beltlocks hold firmly during a randomized X-movement pattern at different speeds and have withstand a lot of ABS printing in during the last days.
Stress testing with random moves @ high speed (240mm/s) in this video
Use the FT8 from this design for a better alignment of the belt.