Hellermanntyton shrinkit 321 a 1 set 385 pieces 380 03003 hellermann tyton 380 03003 p the hellermanntyton shrinkit 321 a 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 p p the black tubes are mainly used for the protection o