Following on from this thread I decided to make another spoke tension tool for myself (having previously made one for a local bike wheel builder). The previous one was based on a length of 25 by 25 box but that flexed a bit under high load so this one is based on 50 by 50 (mainly because that is what I had to hand). I can wind the tension up to the 300Kg max of the crane scale with a plain guage 2mm spoke but a butted (thinner in the middle section) spoke breaks before it gets to 300Kg. The tool doesnt flex at all. The purpose of it is to periodically check the calibration of my Park Tool spoke tension meter - I am pleased to say it is still spot-on after many years of use I think I might treat it to a coat of paint. Relating to the thread above which spurred me into making this - I checked the cheap unbranded crane scale against a better quality branded scale we use for weighing luggage and it is (or one of them is) about 4% out. I think that is good enough for the purposes of this application.