Required on many EZ Classic Lift Frames. they are required when using Sector A Frame (SAF) Cartons 16503 and 16504.16503 uses the 31" ST A Frame. 16504 used 13608 (C Series with 12" PS Rams) and was replaced by 13770 (C Series 10" PA Rams. Refer to Mounting Carton Installasion Instructions for specific vehicle applications. Please scroll through all pictures.