These units consist of a double looped rope line, a release mechanism, and a weak link. This release unit conforms with the requirements of the 1983 amendments to SOLAS 1974. These units will release the liferaft or EPIRB (Emergency Position Indicating Radio Beacon) at a depth of between 1.5 and 4 mtrs underwater. The units could be round or square shape. Below is a reference of brand & manufacturers, but there are specific types of HRU for certain EPIRB brand. Please specify the types and brand when ordering.