The rung in the back of a chair or a stretcher between chair legs may break, even though all the chair's joints remain tight.

Turn a replacement part or use the old one if it can be repaired. You may need to shorten one tenon so you can wiggle the damaged piece into the original position. Drill a 14 " hole into the center of the shortened tenon deep enough to accept a 2"-long dowel and a ballpoint-pen spring. Next, bore a 14 " hole at least 12 " deep into the middle of the plugged spindle hole as shown in the drawing above. Apply glue to both ends of the rung and slip into place as you would reload a roll of toilet paper. The spring will push the dowel into place and, when the glue sets, the dowel will make the repair permanent.
—Earl W. Zieg, Fairfax, Va.