The rail adopts durable metal slider, and a geared drive system which enhances accuracy and speed of adjustment of the rail greatly.This rail with a rubber top surface to protect the underside of your camera.It not only can increase the friction between the rail and camera in order to prevent sliding, but also can reduce camera's abrasion. The design is made in great consideration for your camera. | This 2 way macro rail positioning adopts adjustable locking knob to assure rock-steady focus,a small knob to lock/unlock the current position, and a larger knob that can be turned to move the attached camera in precise increments closer or farther from your subject,rail provides precise scale allow 100mm/3.9in moving leftward/rightward in two directions.Smooth rack and pinion movement provides extremely fine focusing adjustments,great for close-up shooting. | Macro focusing rail slider is essential accessories for macro photography,it helps macro photographers to position camera and focus on subject with the great precision.Suitable for all DSLR or DC with standard 1/4" female screw hole;Two 1/4" male screw are provided, allowing the unit to as a flash bracket. | 1/4" male thread screw compatible with most DSLR or DC;1/4" female thread screw can be attached to tripod head or other compatible devices. | If you purchase two piece macro focusing rail sliders, they can be combined into a 4-direction macro slider. And it can also be divided into two one-way macro slider, it is very simple to mix and split.