Socket Head Fasteners Technical Information

Basics of...Socket Head Fasteners

All Socket screws meet AISI, IFI, ANSI, ASME and ASTM standards and specifications.

Socket screws include several types of high strength fasteners, all using an internal hex drive for installation. Socket head, low head, flat head and button head cap screws are all tensile fasteners. Their clamping strength is derived from stretching the screws and creating “preload�? to combat the external forces seen in the clamped parts. Socket shoulder screws have both tensile and shear applications. Socket set screws are compression fasteners. Socket screws are used in a wide variety of applications where both strength and cosmetics are important. They are found in tooling, metal stamping dies, plastic injection molds, machinery, power transmission, hand and power tools and even furniture.

Socket Head Cap Screws

Socket head cap screws are not grade designated as are hex head cap screws. A standard inch series socket head cap screw is 20% stronger than a Grade 8 hex head cap screw and 50% stronger than a Grade 5 hex cap screw. The tensile strength is a minimum 180,000 psi for sizes 1�?�2′′ diameter and smaller and 170,000 psi for 5�?�8′′ diameter and above (Tensile strength may vary according to heat treatment and manufacturer.) Low head, flat head and button head cap screws are rated 10,000 psi lower due to the head configuration and are seen more in lighter duty applications.

As an alternative drive, Torx Plus (Star Head) screws offer more contact points allowing for a higher level of torque transfer and extended tool life. Additional benefits include faster tool engagement and reduced camout and end load.

Socket Shoulder Screws

Socket shoulder screws have tensile and shear components. The shoulder is precision ground and heat treated and often supports shear loads such as brake pedals, stamping die rails and stripper plates on printing presses. It is that application that helped coin the name “stripper bolts�?. Shoulder screws are called out by shoulder diameter and length and each shoulder diameter has a default thread diameter and length. The default thread diameter for any shoulder is one standard size smaller than the shoulder. For example, a 5�?�8�? shoulder screw has a 1�?�2-13 threaded portion at its end.

Socket Set Screws

Socket set screws derive their holding power from compression of the point into the mating application. The more it is tightened, the greater the axial holding power of the screw. Common applications are shaft collars, crash bars on exit doors and knobs of many types. Set screws are hardened beyond socket cap screws to RC 45-53.

Common Set Screw Point Styles:

Cup: most commonly used style; the thin edge design allows for high holding power for applications requiring quick, permanent and semi-permanent part assemblies.

Cone: highest holding power due to the sharp cone shaped point which allows for deep penetration of the part; commonly used in the permanent setting of parts.

Flat: due to the flat point design, this style is used in applications where frequent adjustments are required and minimal surface damage is desired.

Half Dog: also known as Extended Point or Pilot Point; it features a round nub that protrudes from the bottom of the set screw, thus extended or pilot point. The point is designed to align or mate with a slot.

Oval: like the flat point design, this style is also used in applications where frequent adjustments are required and minimal surface damage is desired

Knurled: the grooves on the cup- point are designed to improve grip and prevent backing out or loosening. Internal and external knurled styled points are available depending on manufacturer.

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