SpecificationOutside diameter:D18 L25Outside diameter:D=18mmHeight:L=25mmMaterial:Aluminum(LY12)Color:silver.The size you can choose:8X8mm6.35X8mm6.35X6.35mm6X8mm6X6.35mm6X6mm5X8mm5X6.35mm5X6mm5X5mmCharacterThe structure is simple，easy to install，buffer，damping，convenient to disconnect.The size is complete and the surface is smooth.Connect servo motor，stepper motor，encoder，screw driving，machine，etc.NoticeThe size is refer to the hole，for example 8X10 is known as one head of the hole diameter is 8mm，the other is 10mmPackage include1X Coupler.(Choose the sizes you want from the drop down list)