just got a new rack set up for my printers with limited space for an external spool holder so I went in and designed a few different types that would fit. the low profile takes up less space while the extended version brings the spool out and holds it flush against the rack this allows the spool (at least in my setup) to feed directly into the back of both of my printers. I have included a support test you can try to see if you need and how each type will affect the print. this test will also make sure the spool holders will mount properly to your shelf. with the attached settings I was able to get a perfect fit and supports were easy to remove. head of spool holder is double sided to hold spool in either direction.