TakTables attach by the long edge with the already included hardware.  This works along the short edge too, but for a really secure attachment, like glued together secure, use a pair of these specially designed short edge connectors.

They are extremely simple to install in seconds, and thanks to TakTable’s unique edge design, they hold 2 tables together like one.

Material will be black PLA.  Inquire about additional colors or discounts on multiples.