This is a belt tension structure along the aluminum bar, the structure also has two similar parts.

Because the print sample uses a slightly low infill parameter, the 3D printed structure after actual assembly is broken when the m3 screw is screwed in.
After calibration, the 3D printed model became more solid.

The remaining parts were 3D printed. The belt tension adjustment screw is an M4 screw and only needs 1 screw.