This is an Y tensioner module that fits Anet A2, Tevo Tarantula and possibly other printers that are using 2040 extrusion on Y axis.
Inspired by Banholm's Tarantula Y tensioner http://www.thingiverse.com/thing:1704100, but I didn't like the size of it... it's HUGE. So I went on to create my own, more compact version, which doesn't share any parts with Banholm's.
The sideplates are same height and just 10mm longer than A2 stock sides (72 vs 82 mm). It has 10mm of adjustment, which is plenty for me.
I printed all the parts with 70% infill and was happy with the results, so didn't try any other options :) With correct orientation all the parts should print fine without supports.
To assemble this, you need 6 pcs of M4x10 or M4x12 screws, one M4x30 bolt with 7mm head and one M4 nut for tensioning, and 6-8 M4x10 bolts+T-nuts for mounting it to the 2040 frame. If you want to use M5 bolts/T-nuts, print with thicker walls (min 1.2) and drill the relevant holes with 5mm drill, should work fine.
UPDATE: Don't use the cheap chinese 16t idler pulleys, they will not last.I'm using 16t idlers in the tensioner, but original flanged 623 bearings would work fine as well. Use the original flanged bearings with a 0.5mm shim between the bearings, otherwise they are too narrow for 6mm belt. Original M3x30mm screws can be used for the idlers, only thing is that they must NOT be tightened, the bearings/idlers must be able to rotate freely, so I suggest using M3 nyloc nuts, 2 standard nuts tightened against each other or a drop of threadlock to prevent loosening over time. I used nyloc nuts.
Easiest is to assemble the inner slide first, then backplate + nut (loosely), then add the sides and mount the whole assembly to the frame.