Now that I think about it, I'm not 100% sure what is going on here, although I know that if we use 1 as the size of the reference head we will get wrong results or in the case of the `spike` head, an infinite loop. We need to create some reference head of arbitrary size so that we can calculate its width. We can't do this before this point, since the width includes the joint which depends on the shaft width. But we don't know the shaft width in `Output` units until we resolve measures. If we used 1 we would actually get a head with a diameter of 1, but the shaft can actually be much, much bigger, easily 20 or 40 and the calculation of the joint width fails. I should probably test this with shafts wider than 100 and see what happens and see if I can figure out exactly what is going on.