Dual linear rails,more stable than single rail version and wheel movement system. No lose in Z height. High-precision linear guide rail runs smoothly with low resistance consumption Applicable models:for Ender3 S1/Ender3 S1 PRO Tip: Do not remove the slider from the guide rail. In the process of taking and installing the heel, the steel balls of the slider often fall out. Due to different production batches, there are two colors of guide rail sliders, black and Green, shipped randomly during shipment, please don't take pictures if you mind Linear Rail:315mm Colour:As Shown Material:plastic+metal Package Contents: 1x Y- double slide rail kit 1x screw package Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.