Update including last two commits

X/Y bars now 170mm long were 175mm, to prevent spectra line rubbing
Fixed hot end double up on overall Bom
Removed redundant bulldog clips
Changed nuts in carriage assembly to M3, were M4
Fixed X/Y end STL's so thru hole is actually thru
Changed hex holes in extruder body to 7.5mm were 8/7.2mm