Our Tuna Mechanism is awesome! The housing is still machined out of a solid stainless steel and fully-rounded ends make it a breeze to install. Internal components have a new geometry for an even nicer, smoother release, strength, and durability. It accepts shaft sizes: 9/32, 5/16, 11/32, and 3/8 with the dimensions of 1"H x 3"L x 0.5"W. Stainless steel pins and line release are included with this trigger mech. For the easiest installation, be sure to get the installation jig for this trigger mech. The tuna trigger mechanism is used by the top speargun builders