This is a motor or shaft mount for a 25mm diameter cylinder. Both parts are necessary. Depending on your setup you may need to scale the parts by 25.4 for a metric conversion. There are general drawings with overall dimensions in inches in the photos above.

The hole is slightly undersized, and fastening the U shaped piece to a board makes the mount act like a shaft collar and grip the motor or shaft. This wouldn't hold against high torque, but can hold or align a motor under low load.

The mounting holes are 1/4" clearance holes spaced 2" apart.

http://bit.ly/25mmMotorMountCAD