Most systems save time in spending turning raw materials into components, but the next production step is often assembling and fastening those additives together. fee, weight, electricity, availability, reliability, corrosion resistance and ease are a number of the many factors that have an impact on the fastening technique. There are more than a hundred particular fastening designs and tens of hundreds of variations when duration, give up and material are counted. 

three factors decide whether or not or not a fastening is a screw or bolt.

• length: Screws are normally under ¼ " in diameter; bolts are large.

• Mating threads: Screws healthful threads tapered right right into a workpiece; bolts healthful into a mating nut. this is generally, however now not always, actual.

• Head design: Screws are frequently slotted; bolts regularly have rectangular or hex heads.

In the passage with the difference amongst stress and head layout, power design is the outside or inner form at the fastening head that couples the screwdriver, socket wrench or distinct using device to show the fastener. the pinnacle design is the general shape of the top that makes the fastener higher appropriate to a selected utility, such as a spherical, flat, oval or fillister head. however, there may be some overlap: All external hex drives are hex heads, but inner hex drives, all referred to as Allen heads, might also take numerous shapes notwithstanding the fact that they're usually called hex or Allen heads. therefore, the ones  terms are indistinct. There are 4 commonplace screw stress designs. Slot heads have a single slot and are pushed through a flat-bladed screwdriver. Their number one disadvantage is they do now not paintings well with electricity screwdrivers due to the fact flat blades have a tendency to come out of the slot and damage surrounding work. Phillips heads, every now and then referred to as pass-head screws, have a “+”-shaped slot. They had been at the start designed to be used with energy screwdrivers in manufacturing. The rounded corners within the device recess make the purpose force “cam out” at the same time as the fastener is tight and moreover makes unscrewing hard. . combo heads receive both a Phillips screwdriver or slot-blade riding pressure. aggregate heads are used quality on screws. Pozidriv heads are similar to Phillips heads however have extra steel-to-metallic contact to permit higher torque utility with out camming out. Phillips’s screwdrivers will normally work in Pozidriv screws, but Pozidriv screwdrivers are probable to slip or tear out the screw head while applied in Phillips screws. it's miles a growing exercise to position Phillips heads on inch-based totally definitely fasteners and Pozidriv heads on metric ones. a ramification of threaded fasteners are available, which includes device screws, gadget bolts, socket head cap screws and bolts. system screws are made in a ramification of head shapes, pressure styles and materials. they're to be had as small as 0.021 " in diameter to 30" in diameter and in lengths from 1⁄8 " to three ". Many people call bolts from ½ " to ¾ " in length screws, however this is technically incorrect. device bolts are most often available in hex or rectangular head patterns in diameters from 30". Mating nuts are to be had for them. Dimensional manage on machine bolts makes them suitable simplest for tough work.