Timing Belt GT2, Printrbot Simple Tension Block 2.1mm

Tension Block for use in Printrbot simple GT2 belt modification by iamjonlawrence
http://www.thingiverse.com/thing:194686
and
http://www.thingiverse.com/thing:194586
The belt and pulleys i bought from amazon.com
http://www.amazon.com/gp/product/B00GNWBUW6/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
must be a little thicker than the one used by iamjonlawrence, when i reflect mine over on to itself to lock it into the block it cannot pass into the narrower side of the tension blo