This part is a plastic coupling for pipes of different diameters. In this case for 13 and 15 mm diameter pipes, the piece allows to place a knob with bolt and nut to adjust the sliding pipe which is the smallest diameter.
Several formats of the piece are included, to be able to modify its measures, if necessary, as well as STL file for 3D printing.
This part can be ideal for adjusting the height of a tripod made by yourself, with pipes that you have at your fingertips.