One of the major flaws with the stock VC4 spool holder is that when the build plate gets low enough, you can no longer remove the spool to replace it.  This mod allows for the arm that the spool rests on to be removed, without tools, from the frame, allowing you to swap out spools and get back to printing!

The spool arm slides into the frame arm, and so there is a bit of a friction fit in this.  I have provided 3 different tolerances on the frame mount, so choose the one that allows for easy removal while also having the least slop in it.  I found the 5.5mm gap tends to be best for non-Carbon Fiber/Glass Fiber filled filaments, and the 5.7mm works best for CF/GF filled filaments.  

This will require you to have your printer pretty well dialed in to get the proper dimensions as it is a tight fit.  Over extrusion or inaccurate dimensions will make the parts incredibly tight, and impossible to remove when actually in a scenario where you are doing a filament change with the bed plate down low.

It does help to install/remove the spool arm into the frame mount several times after printing until it loosens up a bit.  This will make it easier once you actually have to use it in the printer.

Installation is easy - bolt the frame mount portion to the side of the stock extrusion piece used for the stock spool mount using the same M6 bolt and M6 3030 hammer nut.  The spool arm portion then just slides into place.