16-14 to 12-10 gauge heat-shrink heavy duty step-down butt splice terminals. A heavy duty heat shrink jacket makes it very difficult to cut into these heat shrink terminals during the crimping process, a common problem with basic heat shrink terminals. If, in a rare instance, you do pierce the jacket, during the heat shrink process the jacket will heal itself and fill in the hole with sealant. This is the highest quality line of heat of heat shrink terminals available. For use in harsh environments, after crimping the terminal onto the wire, simply apply heat. Keeps moisture out while ensuring your wire does not pull out of the terminal. Requires one crimp on each end plus heat.