So here's the deal. We carry these spring bushings specifically for our 24 inch Reverse Curve Springs and 29 inch Slipper Springs. 9/16 is the go to size for utility and most land trailers. On a boat trailer, you will have 1/2 inch diameter bolts, which would require 1/2 inch inner diameter bushings to keep the bolts nice and snug. If you are purchasing one of those springs and you need them for 9/16 inch, add these to your shopping cart!! Commonly referred to as a Nylon BushingSpring Bushing Measurements:Outer Diameter: 7/8 inchInner Diameter: 9/16 inch