Trailer Springs: There are 3 basic types of springs used on boat trailers. These are: Double Eye, Single Eye, and Hook or Open Eye. The following is some guidance on how to measure each type of spring:
Double Eye Springs (DE) are measured eye to eye
Single Eye Springs (SE) are measured eye to end
Open Eye or Hook Springs are measured Eye to Center of Hook
There are 1 leaf 2, 3, 4, 5, 6, leaf springs. When measuring to replace springs, it is best to measure where they mount hole-to-hole as the old spring tend to have flattened out and are longer that they were when new.