Usually for pipe threads, old school, but some were made for bolt threads as well.. I have a nice, complete set of pipe threading dies and handle that I inherited from my dad, probably about 1900 vintage, still in the original box. IIRC, the dies are about 3 1/2" square.
The modern producers of cheap round dies should take notice of the old square dies.............no matter how cheaply made the holder,they worked OK,unlike the modern round dies that shear a soft screw and turn in the mazak holder at will.
My dads shop had several sets of square dies in two different out side dimensions with ratcheting handles and other hardware. I think they are mostly pipe thread, but I need to take a closer look when I dig them out of the trailer this spring. Kept a lot of his stuff for sentimental reasons. Think I will end up putting a lot of it up on the walls in the new shop. Mike