Application Guidelines

    1-Cap Screw

    An externally threaded fastener normally used in a tapped or blind hole to hold components together. Cap screws are distinguished from bolts by a washer face on the underside of the head and a header point. Cap screws are used when the assembly requires a stronger, more precise and better appearing fastener. During manufacturing, cap screws are held too much closer tolerances than machine bolts and are produced with semi-finished (machined) bearing surface.


    An externally threaded fastener normally tightened or released by torquing a nut. "Designed to hold components together"

    3-Header Point

    A reduction at the threaded end of a fastener designed to facilitate starting in a tapped hole.

    4-Carbon Steel

    Any steel made by combining carbon with iron. The amount of carbon, expressed as a percent determines whether the steel is low, medium or high carbon.

    5-Heat Treating

    Heating and cooling a metal in certain time cycles to obtain specific desirable conditions or properties.

    6-Clamping Force

    The amount of tension force created that holds two or more pieces together when a fastener is tightened. To prevent failure due to loosening, overloading, or fatigue, the clamping force produced must be greater than the external forces applied to that assembly, also defined as preload.

    7-Elastic Limit

    The maximum stress that can be applied to a fastener that will allow it to regain its original dimensions after removal. It is the maximum stress that can be applied with no significant measurable after effects. Once this value has been exceeded for a fastener, the fastener becomes permanently elongated and will not return to its original dimensions.

    8-Proof Load

    The load just under the yield strength that can be applied to a bolt with out causing permanent set greater than .0005". This is the maximum SAFE load that the bolt can support. Torque value is established taking proof load into consideration.

    9-Yield Strength

    The load "usually expressed in psi" that is necessary to stretch a fastener to the point where, after the load is removed, the fastener will not return to its previous length.


    A load that is applied in line with the center line of a bolt that stretches it.

    11-Tensile Strength

    The load in pounds per square inch (psi) required to cause failure in tension (stretch).


    Force exerted 90 degrees to the center line or length of the bolt that tends to cut the bolt into two or more pieces.

    13-Shear Strength

    The amount of force usually expressed in psi required to shear the bolt into pieces. This is referred to as single shear and usually has a value of about 67% tensile strength. Double shear is where shearing forces are applied at two points along the shank of the body cutting the bolt into three pieces. Double shear strength is usually about 175% of tensile strength.


    Annealing is a heat treatment process of relatively slow cooling after holding the material at the annealing temperature for one hour for each inch of the maximum section being treated.


    A secondary heat treatment process used on already hardened alloy steels in order to reduce the hardness and brittleness and increase the toughness. In general as hardness is reduced so is the tensile strength but the ductility is raised.


    The rapid cooling of a heated metal by bringing it into contact with liquids, solids or gases.


    The deepest point of the V - notch that forms the groove of a thread, a well designed fastener should incorporate a radiused or rounded root.

    18-Minor Diameter

    Smallest diameter of a screw thread, "the distance across the base or root of the threads of a bolt"

    19-Major Diameter

    Largest diameter of a screw thread, "the distance across the crest or top of the threads on a bolt"

    20-Pitch Diameter

    The diameter half way between the major and minor diameters.


    The number of threads in one inch of the threaded length of a fastener, expressed as threads per inch (TPI). The pitch of one thread is the distance that a nut would advance on a bolt when turned one full turn. In metrics the pitch is determined by measuring the distance between the crest of one thread to the adjacent thread, this value is expressed in millimeters (mm).

    Fastener Facts

    Grade 2 Bolt

    ¼" - ¾" (6" length or shorter)=74,000 psi minimum
    ¼" - ¾" (longer than 6")=60,000 psi minimum
    Over ¾"=60,000 psi minimum

    Grade 5 Bolt

    ¼" - 1"=120,000 psi minimum
    1" - 1½"=105,000 psi minimum

    Grade 8 Bolt

    ¼" - 1½"=150,000 psi minimum

    Socket Cap Screws

    Up to and including ½"=180,000 psi minimum
    Over ½"=170,000 psi minimum

    B7 Fasteners

    Up to 2½"=125,000 psi minimum

    Tensile Strength - Metric Bolts

    Class 4.6=58,000 psi minimum
    Class 8.8=120,350 psi minimum
    Class 10.9=150,800 psi minimum
    Class 12.9=176,900 psi minimum

    Similarities between Metric classes and Standard grades

    • Class 4.6 is similar to A307-A (Grade 2 Hex Bolts)
    • Class 8.8 is similar to A449 (Grade 5 Cap Screws and Hex Bolts) and A325 (Structural Bolts)
    • Class 10.9 is similar to (Grade 8 Cap Screws and Hex Bolts) and A490 (Heat Treated Structural Bolts)
    • Class 12.9 is similar to (Alloy Steel Socket Head Cap Screws)

    Standard inch Socket Head Cap Screws are not Grade 8 fasteners.

    They differ from Grade 8 fasteners in the following ways:

    • Tensile Strength (Sockets are stronger)
    • Hardness (Sockets are harder)
    • Head markings (Sockets do not have specific head markings)

    Tensile Strength - Non ferrous Fasteners

    Pure Copper=30,000 psi minimum
    Brass=55,000 psi minimum
    Silicon Bronze=70,000 psi minimum

    Head Markings