In my rendition of this awesome accessory, I have lengthened the end so that the spool is less likely to "jump" off should there be a tight spot during printing (this has a negative effect should your spool have a narrow hole).
I also modified the post to allow the bearing to snap in and snap out so that it doesn't come off accidentally while rolling.
I use a rubber band to hold the 2 parts together under tension.
Updated 06/08/2019 - Changed to post style, recommend printing at 20% infill and 4 walls. When placing the bearing press it straight down, no to push at any angle or you risk breaking off the tab.
Updated 07/28/2019 - Changed the back bearing to extend up and down past the spool axle. This prevents the spool from jumping off when it gets towards the end of the spool and is very light.