When measuring springs the trailer should be unloaded. When determining the length you measure from the center of one spring eye to the other (straight across) as well as along the contour of the main leaf ; see diagram - measurements (a) and (b). To maintain the correct capacity you need to also measure the thickness of the individual leaves as well as the width. Measurement (h) gives you the free arch. Most standard springs come with bushings to accept 9/16" bolts.