The 9742 Quasi-kinematic, quick-release Rail Carrier has a spring-loaded lever that allows it to be locked in place without introducing motion. An 8-32 screw permanently locks the carriers. Model 9742 has an array of 8-32 and 1/4-20 threaded and counterbored holes and is 3-in. long. It works with 9731 or 9732 optical rails.