Greg's Wade extruder idler for 40mm M3 bolts
I haven't been able to source M3 bolts longer than 40mm locally, which meant I have previously had to use tiny, weak, tensioner springs.
This version of the idler has a cutout so that there is enough space to use decent sized springs, so now I have good control over the tension.
I printed it on it's side for extra strength, with (Kisslicer medium) support, 3 loops and 100% infill.