They are put together using small sunken brad nails...we monitor the chins chewing on them and they all seem to chew around the edges where there are no nails. We tried the non toxic wood glue and dowels, but they still collapse in a cage with hyper chins. These have the strength to hold up the pick up truck! This way we don't have to worry about a chin jumping on the top and having it collapse with a chin inside. When it gets chewed too much, it gets replaced...Usually they can last between 6months to a year before needing replacing depending on the chins chewing.