Hellermanntyton shrinkit 321 a basic 380 03004 hellermann tyton 380 03004 p the hellermanntyton shrinkit 321 a basic is dual wall heat shrink tubing with a 3 1 shrink ratio the attractive and reusable kit is ideal for assembling and identification the inner wall melts when heated and is forced into gaps when the tubing cools down the adhesive forms a seal preventing any moisture seeping in thus protecting the components the black tubes are mainly used for the protection of connectors