The Using Your Least Useful Part challenge for me was mandatory as I set the challenge. I was immediately confronted with the difficulty of a suitable least useful part. Ideally the dog clutch would have been used, as this never was satisfactorily used in my most recent model, the fruit machine. However I quickly realised I did not have the parts to build anything reasonable.
Another part which did not come to any use in the fruit machine was the single bent strip (part 102). There are a lot of close spaced items in the fruit machine and the narrowness of the single bent strip seemed appropriate. In the end however it was only used as a stop to a counterbalance and could probably been substituted for any number of parts.
However a single bent strip is very good at carrying pulleys without a boss and so I decided on an armchair with castors. The single bent strip forms the base of the castor with the centre hole being bolted to a long threaded pin as the vertical swivel. The pulley must be off centre, so 1” corner brackets are bolted to the single bent strip and the pulley attached to the other remaining hole.
The armchair works very well, turning in all directions.