A Square Head Bolts are low or medium carbon steel, externally threaded bolt, 1/4″ diameter or larger, with a trimmed square shaped external wrenching head. Square head bolts were the industry standard prior to hex bolts taking over. A square head bolt has a distinctly shaped head that makes it ideal for working in blind areas. Square head bolts are now normally used in rustic look applications.
With the proper tools, tightening a square head bolt is easy even when the fastener is out of your line of vision.
The head design of square head bolts enables an easier wrench grip for nut tightening. They are usually used in new construction to mimic an older aesthetic or in railway applications. This shape of the bolt head is also easy to check visually. The flat sides make it simple to gauge whether the bolt has been properly tightened since the sides will align with the materials being fastened. Square head bolt design enables an easier wrench grip for nut tightening. They are usually used in new construction along with square plate washers and taper washers.
These Bolts worked really well in the railroad industry, where supervisors could check that all bolts were on based on whether the head lined up with the tie. It is common in the railroad industry, on electrical panels, and in furniture manufacturing.