SCS12UU is an closed type linear ball bearing with Aluminum block mounted. The inner diameter (which is the same as the shaft diameter) is 12 mm. It can be mounted on 12mm linear shaft. It is very common choice for linear motion applications.  

The linear bearing sliding block (sometimes called pillow block) is composed of two main parts: linear bearing and self-aligning aluminum block. The self-aligning aluminum block allows for compensation of any misalignment of inaccuracy in the final assembly. The bearing cage made from special polymers allowing for smooth and noiseless operation.  

It is ideal and low cost solution for CNC and other machinery applications that require smooth motion with minimum friction and at the same time high rigidity and less vibration with affordable cost and easy to assemble operation.  

Linear Bearing Block SCS12UU dimensions and datasheet