Lots of trickery in our spring sliders. This is the smoothest and most stable slider on the market. We use a linear DU bushing on a hardened shaft, along with a shaft stabilizing internal piston. A four position locking mechanism assists with fine tuning. The Torrington bearing on the adjuster nut allows for easy adjustment and bind free spring travel. This is our 21” extended ALUMINUM fine thread body for 2 1/2" OD springs.