Square head bolts are typically lag bolts. These lag bolts resemble very large screws and are used when assembling heavy lumber. The advantage in using square head bolts is that they can be tightened with an adjustable wrench. Using the wrench, the square head bolts are easily tightened in close quarters where other tools cannot be used.
Sond Nuts and Bolts manufactures high quality Square Holding Down Bolts also known as Foundation Bolts which is widely used for holding down steel-work frames to concrete bases. These bolts are manufactured using high quality Steel Grades 4.6 and 8.8.