Compact Bowden Extruder 4mm Idler arm with lever

Billies idler arm clearanced for the big fitting on mokash770's extruder frame. Also enlarged the hole for the m3 screw head to fit washer. Redesigned lever to a larger one angled so there's more room to get in between it and the filament entering the extruder.

Uses M5 bolt up to 12mm with washer to retain the bearing, or print the push-fit retainer (inspired by https://www.thingiverse.com/thing:287287).