Update: These won't fit on the 'Y' belts on newer UM's.
See Notes and Picture in the comments below.
Main picture here shows a clamp on the 'Y' belt of an older UM.

Parts required per belt

4 - M2.5 X 8mm small head screws. - ebay.com.au/itm/300521403792?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
1 - M2.5 X 30+mm screw. (35mm used here) - ebay.com.au/itm/370568422906?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
5 - M2.5 thin nuts - ebay.com.au/itm/120894813183?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649


Instructions

* Print 2 X Nut Side and 2 X Screw Side clamps for each belt (in there current orientation) and clean out with a 2.5 mm drill.
* Work out where the outside pair will clamp to the belt and move the spot to the centre.
* Twist the belt to assist in putting the clamp on.
* Push through the adjusting screw all the way through the bottom clamp.
* Place the other bottom clamp on the adjusting screw.
* Put the nut on the adjusting screw a few turns and slide the free clamp up against it.
* Clamp the top clamp onto the bottom clamp.
* Tighten the adjusting screw and twist the clamps so they are horizontal.
* Test tightness and adjust.


Hint

Over tightening makes it harder to move the extruder so test it still moves freely after tightening.