Knobs I designed for Things I designed. The knobs thread onto the rod . The rod needs to be ground on the sides or roughened in some way first . You need to clamp upright protecting the threads then heat the rod with a torch or heat gun before screwing on the knob . You may be able to screw the knob on first then place in an upright position . The rod is heated to melt the pla just in the center enough that it conforms to the flats or marks in the threaded rod . Then let it cool in an upright position until the rod is cold . Then you have a threaded rod with knob on the end !