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"
A reduction at the threaded end of a fastener designed to facilitate starting in a tapped hole.
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.
Heating and cooling a metal in certain time cycles to obtain specific desirable conditions or properties.
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.
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.
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.
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.
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.
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.
Smallest diameter of a screw thread, "the distance across the base or root of the threads of a bolt"
Largest diameter of a screw thread, "the distance across the crest or top of the threads on a bolt"
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).
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
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