After putting together your anet a8, you may have realized that the Y axis belt runs in a triangle. the mounting point to the bed is too high, so the belt can't run in a straight line from the motor to the pulley/belt tensioner.
This fixes that.
The belt running in a triangle, causes the bed to travel different lengths, depending on how far it is from one of the edges, it should move the same distance regardless of its position.
The clamp has precisely modeled GT2 belt profile grooves, to grip the belt as well as possible, you only need to insert ~5 'bumps' on the belt for it hold. Remember to screw it down hard enough. Inset the belt on each side, so that there are 1 or 2 grooves left in between.
You can reuse the original screws, they're just long enough.
Print so that the belt grooves are facing up.