Davinci X belt manual tensioner with bearings

The standard item has a spring and a pathetic screw to keep the tension on the belt. I found the screw would tire and then the belt would loosen under load as the spring let it go.

This is a remix of the belt tensioner http://www.thingiverse.com/thing:805215 that uses 2 x MR63ZZ (3x6x2.5mm) ball bearings mounted on the stock pulley and the original spring.

This version uses a 20mm M6 bolt through the end, it's much easier to fit - Simply loosen the bolt right off, push it all the way in,