Machine bolts have a variety of different features. Machine bolts can be cut with fine or coarse threads that extend in length from twice the diameter of the bolt plus ¼" to twice the diameter plus ½" (depending on the length of the bolt). They come in a many different types including stainless steel, brass, silicone bronze, and zinc plated bolts.
Machine bolts are made from multiple metals and are applied, hence the name, metal to metal which is commonly found on different types on machines. Machine bolts are made from a variety of types and grades to suffice for the abundance of applications machine bolts are used.
Common bolts types include silicone bronze, brass, stainless steel, and zinc plated bolts
Zinc plated bolts: Steel that is zinc plated. Zinc plated inserts offer moderate protection against rust.
Stainless steel 18-8 bolts: This alloy of steel has a high corrosion resistance.
Brass bolts: An alloy of copper with good corrosion resistance. Once common, now being replaced by stainless steel.
Silicon bronze bolts: An alloy of copper with a greater strength and corrosion resistance than brass.
Machine bolt heads can be may be square, hexagonal, rounded, or flat countersunk. Machine bolts are made in diameters from ½" to 3 inches depending on the length desired for each application.