H4 Boa® Coiler Closure System - Precision speed lace system with a reel that retracts slack in the cables. Quick, durable and easy to use. The internal workings of H4 feature an updated cartridge assembly for unprecedented durability, with a new breakaway design that is engineered to defy failure. The cartridge ejects on severe impact without damage and is easily reinserted into the system – anytime, anywhere.