B2D - a few parts modified

I really love the original design of the B2D feeder. It's compact and excellently designed. There were a few improvements I made on the parts that were derived from my workflow that may be useful to others.

For 1.75mm files:
1) Nut and bolt were changed to accommodate a #10 nut with a button head screw
2) Bearing mount and spring housing were modified to have a larger finger pad to more easily squeeze the spring to manually load/unload the length of the bowden tube
3) Two alternative filam