The 4 stalls in our trailer were custom made to fit and are each 21" wide and the metal mesh dividers are about 11" from the bottom we always drive them tied they can't turn around or rear up and they have never fallen down because they have the sides to brace themselves on it's easy on legs ribbed rubber matts are under the shavings and poop stays behind them...plus a cam up in the truck is a handy way of keeping an eye out for anything that could go wrong back there. Like the mare who had her slinky get into her eyes making her blind when she was rubbing her head on the divider so we pulled over and fixed that for her before she panicked..