The dowel pin is 1/4 inch diameter, SAE thread. You have to use a nut in the top frame to secure it. Go to the hardware store and get a hex flange nut. Think of this as a 6 sided nut with an attached washer. Position the top somewhere between raised and lowered position so that gravity will not move it either direction. Small fingers help to get the nut into position so that you can tighten the dowel pin.