I have one of those metal clotheshorses but the plastic clips to hold the two sides together have long since broken meaning that I have to prop it up and try to stop if falling over.
I made this using the great OpenSCAD. The reason it is great is that all the core dimensions can be defined at the top of the source file (washclip.scad), then all other dimensions are calculated from these. Then you can just update these dimensions and the model will change!
// Radius of the clip holes
hole_r = 2.5;
// width of the passage to the hole
hole_opening = 2;
// How wide the clip is
clip_width = 30;
// How \'chunky\' the clip is
clip_thickness = 8;
// distance between the centres of the two holes
clip_length = 14;