I use Greg Frosts' gear library all the time, the code module you want to execute needs to be run - there are working examples in the code, which take the module defaults... bevel_gear ();  //runs the code... but it runs with the parameters set in the bevel_gear module - this is a working example of the modified parameter set I use.. bevel_gear_flat = 1; bevel_gear_back_cone = 1; module bevel_gear (     number_of_teeth=30,     cone_distance=115,     face_width=8,     outside_circular_pitch=550,     pressure_angle=30,     clearance = 0.2,     bore_diameter=11.2,     gear_thickness = 10,     backlash = 0,     involute_facets=0,     finish = -1) It will only generate a gear if you press F6. Roger.