We carry these spring bushings specifically for our 26 inch Reverse Curve 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.
Commonly referred to as a Nylon BushingSpring Bushing Measurements:
Outer Diameter: 1 inch
Inner Diameter: 1/2 inch
Length: 1 3/4 inch