These can be screwed into each end of a cable if you need to use the tips for another project. This will hold your current project on the cable while you use the tips for another project.
Red stoppers (mini) are for tip sizes 000/1.75mm to 1.5/2.5mm
White stoppers (small) are for tip sizes 2/2.75mm to 8/5mm
Black stoppers (large) are for tips sizes 9/5.5mm to 15/10mm
Made of resin.