Typically, metal special fasteners are more costly than standards because they are made through hot or cold forming. This requires more precision, manufacturing operations, highly skilled workmen, and initial engineering. The payoff is in performance and lower cost.
Metal special fasteners are divided into two general categories. First, there are modified standards, fasteners that have been changed slightly in shape or mechanical properties to meet a specific need. For example, a standard hex bolt may be specially hardened or lengthened or have a slot machined in its tip. The other type of special might be called a multiple-function fastener. These fasteners perform some function in addition to fastening. They are incorporated into gears, cams or levers, or contain some other machine element critical to the product.