~ Article courtesy of UC Components
Did you know the first known recorded use of screws occurred during the time of the ancient Greeks? These early fasteners were used in devices to press olives and grapes. From those humble beginnings, screws have become one of the most widely used pieces of manufactured hardware.
And today, these fasteners are available in several types, ranging in style, shape, size, and material. One of the top considerations when choosing the fastener for any application should be the type of screw head selected for use.
Here’s a brief overview of some of the most common screw head types, including their typical applications.
Socket-head cap screws are machine screws with a cylindrical barrel-shaped head containing a hexagonal socket that fits a wrench for turning (instead of a slot or external hexagonal). These properties mean that socket-head cap screws are ideal for use in confined spaces. Socket cap heads are small, so the size of the component parts can be reduced, saving material costs. Smaller parts cost less to drill and tap, take less energy to drive, and weigh less than alternatives.
Button-head socket cap screws have a rounded, low-profile head containing a hexagonal socket that fits a wrench. These screws offer a flush profile, making them ideal for use in areas with little overhead or clearance and in confined spaces. They work best in light-duty applications such as in removable panels. Their wider bearing surface and high-tensile strength mean they’re also reliable in security applications.
Socket set screws are typically used to secure an object within or against another object. They’re commonly used to secure a pulley or gear to a shaft, serving well in confined spaces. These fasteners are headless, meaning the screw is fully threaded and has no head projecting past the major diameter of the screw thread.
A socket set screw contains a hexagonal socket that fits a wrench instead of a slot or external hexagonal, and fastening these components requires no external clearance. The socket set screw passes through a threaded hole in the outer object and is tightened against the inner object to prevent it from moving relative to the outer object. It exerts compressional or clamping force through the bottom tip that projects through the hole.
Flat-head socket caps feature a low-profile and countersunk head. They’re ideal for applications requiring a strong fastener with a flush mount and are often used in applications that require moving parts to pass over a fastened area. Thanks to their ability to mount flush with the surface, flat-head socket caps are less apt to snag objects moving overhead. They’re produced with a socket drive that contains a hexagonal socket to fit a wrench for turning.
Flat-head Phillips screws have a low-profile and countersunk head. They feature similar characteristics as the flat-head socket caps and are ideal for applications requiring a strong fastener with a flush mount. Flat-head Phillips screws have two partial slots crossed at right angles and are driven by a special screwdriver called a Phillips screwdriver.
An advantage of the Phillips system is the screw and screwdriver, when used together, are self-centering. The x-shape of the screwdriver head fits into the similarly shaped slot of the screw, which is held in place so the force of the torque is centered naturally. This ensures the screw is driven straight.
Flat-head slotted screws are also ideal for applications requiring a strong fastener with a flush mount but are typically used in projects with moving parts that must pass over the fastened area. These screws are manufactured with a slotted head drive. Slot screw heads have a single horizontal indentation, referred to as the slot.
The fastener head is driven by a “common blade” or flat-bladed (flat-head) screwdriver. The slot has a flat bottom, which is a good choice for low-torque, low-speed applications.
Pan-head Phillips screws take their name from the appearance of their head, which looks like an upside-down frying pan. This is a common head type of the non-countersunk used in machine screws. They have wide heads, a flat bearing surface, high vertical, chamfered, or curved sides, and a flat or slightly domed top.
A pan-head Phillips head has two partial slots crossed at right angles, driven by a special screwdriver called a Phillips screwdriver. As mentioned, this system is self-centering.
Fillister-head slotted screws have an oversized head, which is ideal for counterbored holes. These fasteners are like pan-head slotted screws but with greater side height. Fillister-head slotted screws are also compared to cheese-head slotted screws because they have cylindrical sides and a flat mating surface. But where the cheese-head slotted has a flat top, the fillister slotted screw head has a domed top resulting in an overall deeper head (these fasteners are sometimes called raised cheese-head slotted screws).
The fillister is manufactured with a slotted head drive. Slot screw heads have a single horizontal indentation referred to as the slot with a flat bottom, which is ideal for low-torque, low-speed applications. The fastener head is driven by a flat-bladed (flat-head) screwdriver.
Hex-head screws, also known as hex bolts, are bolt fasteners with a six-sided hexagon head and an externally threaded body. The hexagonal profile enables easy wrenching while ensuring enough torque to the bolting joint. Hex bolts are typically used with a washer and hex-nut assembly or a tapped hole. Hex-cap screws allow for greater torque than conventional screws with a circular head.
Twelve-point flange head-cap screws, also known as 12-point bolts, are an alternative head design for hex socket-cap screws. The flange diameter and head height are designed to fit a range of applications and counterbored holes made for standard hex socket cap screws.
The 12-point design permits this style bolt to be tightened with a 12-point socket wrench, which allows for the application of higher torque than a standard internal hex-drive socket head-cap screw. Another advantage: the 12-points have 30° between flats (as opposed to hex heads, which have 60°). This enables increased wrench flexibility (or placement) when manipulating the fastener.
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Filed Under: Fastener Engineering • Screws, Fastener screws • nuts • bolts
Tagged With: uccomponents
