The 9741 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 9741 has one 1/4-20 threaded and one 1/4-20 counterbored hole and is 1 inch long. It works with 9731 or 9732 optical rails.