The primary function of an retractable block is to arrest a fall by quickly activating the braking mechanism when it detects sudden movement or acceleration. This rapid response helps minimize the potential for injury due to a fall.

Retractable block are designed to maintain constant tension on the lifeline, helping to minimize slack and reduce the risk of tripping or entanglement during use.

Unique to this unit is a spring at the base of the cable to stop it locking permanently if accidentally fully retracted. The user can simply push in against the spring to release the cable again, unlike other models which require the entire unit to be disassembled.