These shipping boxes have a nominal inside length of 20" to 22". They are rated for their stacking and bursting strength to determine the amount of weight they can hold. Single Wall is made of one fluted layer of paper glued between outer linerboards for supporting lightweight items. 32 ECT withstands an edge crush force of 32 lb/in. RSC (regular slotted container) is the most common closure style with flaps that are one half the box width so that they meet in the middle when closed.