The Apeks RK3 fin design has been the standard for Military, Special Ops, Coast Guard, and Public Safety Divers for decades. It is a traditional all rubber design. The RK3 blade material is formulated to hold up in the toughest environments, temperatures, and abuse. The short wide blade provides maximum forward thrust while maintaining great maneuverability. The vented blade design reduces resistance on the upstroke and enhances thrust on the downstroke. The fins come standard with stainless steel spring straps.