Spool holder and filament guide to be used with 2 2020 vslot extrusions spaced 20mm apart. Spool holder is set back so filament travels through the filament guide with standard spool sizes. Remove spool holder quickly just by sliding apart .Spool holder can also be slid on rail. filament guide will slide with filament. Works great,fits great. Solidworks files included so you can modify as you like. Print at at least 40-50% infill so theres no risk of breaking. At 50% its very beefy.