These are 4 start 8mm pitch leadscrews with a 200 steps per revolution motor and the 16x microstepping on most common 3D printers. This adds up to 400 steps per mm 3200 steps/ 8mm per rev = 400 steps /mm the same as most 3d Printer lead screws use. SpecificationsLead screw Materialstainless steelDiameter8mmLead2mmTotal Length400mmScrew nut Material:brassDiameter8mmMounted ball bearing Materialzinc alloyBore diameter5mmHole diameter8mmTotal length55mmHeight29mmShaft coupling MaterialaluminiumShaft6.35 x 8mmLength24mmDiameter18mmQuantity1 set ( 1 screw 1 Screw nut 2 Mounted ball bearing 1 shaft coupling)FeaturesScrew mainly used in stepper motors, machine tools, and other CNC equipment.Screw directly connected to bearing.Suitable for Industrial automation equipment, stepper motor rails, 3D printers, engraving machines, XYZ modules, slider, lifts etc.What’s in the box?1 x Lead screw1 x Screw nut2 x Mounted ball bearings1 x Shaft couplerResourcesHow to install:1. Put screw nut onto the Lead screw.2.Then the 2 Mounted ball bearing separately, install at both ends of the Lead screw.3. According to the size of you need to adjust the distance between the nut and Mounted ball bearing.4. Put shaft coupling into the Lead screw beside the Mounted ball bearing.