Geeetech

You can find them on eg. Aliexpress or eBay by searching "Bushing Axle Shaft Sleeve". Just make sure you get the 8mm ones.

You are most likely angling the Z-axises towards the middle when you're tightening the x-axis belt. I'd recommend putting the locking rings on the insides (thus securing the ends where they are) and THEN installing and tightening the x-axis belt.

Assembly of the Geeetech Prusa i3 Pro B Acrylic (GT2650 board) 3D printer kit, footage heavily edited (removed the boring parts) and timelapsed at 2x speed:

https://www.youtube.com/watch?v=wstxURxdgY4

I will follow up with another video once I've used it for a while

/Linda