Re the crankpins. I am thinking of measuring the nuts. Over the flats and over the width of the points. Pick a drill about half way between. Drill GENTLY, with a pinchuck, deep enough to fit the nut. Run a bolt in from the front, with a washer, into the nut, and try to draw it into the back of the wheel. If it won't go, I'll use the next sized drill to just barely open the recess, rinse, repeat. I am not wild about the idea of applying a soldering iron to the nut, but it may come to that. I have a soldering station, with a rheostat to control the heat. I can start low, and hopefully not over power the plastic. If I were at all proud, I'd use a bush from Gladiator, into a hole bore right thru. But I have no pride.Ah! The wheels on the axles AFTER fitting the conrods. Brilliant! I am concerned, on so many thing, but on the drilling of handrail knob. I've done it before, but that does no relieve the apprehension. What do you mean by a "tread"?