I have OEM quality belts for the GlowForge. There are two Side Tension Belts and one Carriage Plate Belt per GlowForge.
The Side Tension Belt move the gantry forward/back.
The Carriage Plate Belt moves the head plate left/right
These are a heck of a lot cheaper than Etsy sellers I have seen.
Sold each. The Carriage Plate Belt can be trimmed to the Side Tension Belt length if you only want to keep a single belt as a spare.
My belts do not come with the reusable metal bridge assembly. You reuse your original.