This table clamp for holding cables, wires, etc. is designed parametrically so you can specify in the Freecad design (.fcstd file) the exact width of your table.

To do that, open the file in Freecad (it is free and open source) Open the sketch in it (double click the first sketch icon in the left view) and just set the width by double clicking its marker and edit your value in mm. Then File→Export to STL.

The fixed STL is for a width of 35 mm (the actual width is 35.3 mm for some tolerance)