smooth_rod_d      = 8;
threaded_rod_d    = 10;
tie_wrap_w        = 5;
tie_wrap_t        = 2;
washer_d          = 21;
height_of_threaded = 26.5;
height_of_smooth = height_of_threaded + 11 + 9;
height_of_post = height_of_smooth+2;

belt_width = 6.5;
belt_tooth_distance = 2;
belt_tooth_ratio = 0.5;
belt_thickness = 0.8;

idler_bearing_inner_d = 4; // 624 bearing