These are cast sections that very in length from 5' to  25'6" and along with additional extension sections you cut to length and add the transition end sections. You get 2 lengths  25' 6 " long ( 3 -  8'6" segments ) and 4 transition end sections. These pieces were designed to
fit the standard roof body for the Walters narrow cross section

Extensions may be added to the increase the length. Choose
the size you want from the drop down menu for DM 252A.