I was previously using some M3x40 bolts for tensioning the idler on my Airtripper extruder, but needed to scavenge the long bolts for a different project. This idler was designed to allow for the use of shorter bolts. I'm currently using 30 mm bolts with springs, but you could use shorter ones (down to ~20 mm) depending on if you're using springs and their sizes. Hope that this might help someone else. This Thing was modified from the "Airtripper Bowden Extruder BSP Edition" Thing, but should fit most variants of the Airtripper Extruder. As requested in the comments, the lip for the tensioning bolts has been extended and a recessed spot for the washer/spring has been added. I haven't printed this, but it should print fine. Download the R001 files for this version. The photo has not been updated. Sliced with 0.2 mm layer height, 3 perimeters, and 50% infill.