Dual-spring guide rod system gives smooth gentle slide movement to significantly reduce muzzle flip and felt recoil. Proprietary tuned springs help control muzzle rise to get you back on target faster. Primary recoil spring absorbs initial slide movement as the secondary spring gently slows and stops the slide. Softens initial chambering impulse to gently strip rounds from magazine. Improves feeding reliability reduces sensitivity to magazine lip style. Twin-Pack contains one light system and one heavy system. Shooter preference and experience will help determine choice of heavy or light system. Mfg: Sti Steel blue finish. Fits 5'''' barrel guns. Includes full length guide rod main and secondary springs recoil plug and take down tool. Light - Comp guns and 9mm plus guns with lightened slides require light system. .40/.45 caliber guns with a loose-fit slide can use the light system. Heavy