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.
White stoppers (small) are for tip sizes 2 (2.75mm) - 8 (5mm). Black stoppers (large) are for tips sizes 9 (5.5mm) - 15 (10mm). Made of black or white resin.