Effective now, Kirby Morgan has discontinued P/N 545-100 Chin Strap.
P/N 545-100 Chin Strap was an early design that attached to the neck dam/ring assembly on the metal bottom helmets (SL 27, 37, 47, etc.).
It shipped on all helmets, except SuperLite® 17s A/B & C, between 1992 to 2006. The change from P/N 545-100 chin strap to the current chin strap, P/N 505-111 (mounts to the shell interior), took place at the end of 2005. However the part was kept as a spare part.
Kirby Morgan® helmets have been equipped with the current, interior mounted chin straps since 2006 (exc. 17C- 2011). This chin strap is able to retain the helmet to the diver’s head even if the neck dam/ring assembly somehow separates from the helmet. This is because it is mounted to the helmet shell. The 545-100 Chin Strap does not have this ability.