Last Friday we finally decided to fix my Haas VF-3 Mill. It had been tapping very poorly and it turned it was because of this tiny belt that was 30 years old! The belt itself was very cracked and had completely worn out the driven gear. This little belt runs an encoder which needs to sync up with the Z axis so it can feed in and out of the part without destroying everything. There was so much slack in the belt that it was cutting on the way into the part AND out. It now taps like a brand new machine.

The thing in the black posts is the encoder.
This part spins together with the spindle and drives the encoder.
The little guy on the right was way overdue for replacement. You can see how the aluminum wore from where the teeth originally were!!!