This collar is used with my A1 mini along with a low friction spool holder to keep the spools straight - without the collar spools tend to turn sideways , which might lead to a spool falling off.
The radius of the inside curve is 42mm so it should work with other spool holders.
I am using two - one either side of the spool - the outside one has two grips attached to give it more weight low down and prevent excessive rotation.