Back in Feb when I started planning my OX build I ordered some Gates GT3-3mm pitch timing belt, they finally arrived. I am opting to use this belt in an effort to minimise belt stretch especially since I'm using 1500mm rails for my y-axis. Please don't interpret this statement as saying standard GT2 belt is substandard for the task, just that the GT3 "should be better". I found this chart online comparing HDT, GT2 and GT3 belt. Because of the long delivery time I decided to order a few extra belts, if you'd like some send me a message. They are supplied as 1692mm closed loop belts, 6mm wide. They work with GT2 pulleys.