**Clamp Force:** The compressive force on the joint members that results from the tensile force developed in a tightened bolt. This force, not torque, is what holds your bolted joint together.

**Design Tension:** The tensile force on the bolt, measured in klbf or kN, at which SmartBolts® are designed to indicate the “Tight” color. “Tight” shows the bolt has been properly installed and Preload is established. All of the SmartBolts® products listed in this catalog have an indicating Design Tension of 70% of fastener Modified Proof Strength.

**Elastic Interaction:** In a bolted joint with multiple fasteners, the variation in individual fastener preload due to tightening of the other fasteners.

**Embedment:** Localized yielding of bolted joint components resulting in a change of grip length consequently causing relaxation of the bolted joint.

**Grip Length:** The combined thickness of all components joined together between the bolt head and nut. Given in inches for Inch series SmartBolts® and millimeters for Metric series SmartBolts®.

**KIPS:** A non-SI unit. 1,000 pounds-force, used primarily by American architects and engineers to measure engineering loads

**klbf (kilopounds-force):** A measure of tensile force or clamp force on a bolt as it is tightened. 1,000 pounds-force. The symbol KLBF is used when it is necessary to clearly distinguish it as a unit of force rather than mass. The name comes from combining the words “kilo” and “pound”; it is occasionally called a kilopound.

Design Tension, Proof Strength, and Ultimate Strength are expressed in klbf for Inch series SmartBolts®.

**kN (kilonewtons):** A measure of tensile force or clamp force on a bolt as it is tightened. Design Tension, Proof Strength, and Ultimate Strength are expressed in kN for Metric series SmartBolts®.

**Minimum Grip Length:** With respect to SmartBolts® in this catalog, if a Minimum Grip Length is denoted, there is a limit to how far the nut can be run up the shank during installation before it begins to impact the accuracy of the SmartBolts® indicator. Customers may contact the factory to learn what the specified minimum grip length is for a particular SmartBolts® model, if it applies.

**Modified Proof Strength:** The proof strength of the bolt after conversion into a SmartBolt. In all but the shortest bolt lengths listed in this catalog, this strength is identical to the bolt proof strength before modification.

**Nut Factor:** A constant that attempts to model all of the many variables (such as friction) that affect the torque-tension relationship. Torque charts depend on an assumption of the nut factor, but it is very difficult to predict and measure. SmartBolts® eliminate the nut factor from the bolting equation, measuring and displaying Tension directly.

**Preload:** The tensile force developed during installation (tightening) of a bolt. This load can be directly measured and displayed by the SmartBolts® indicator.

**Proof strength:** The tensile strength of a bolt beyond which permanent elongation of the bolt may occur. SmartBolts® are designed to operate in tensile loads from zero up to proof strength. This is called the elastic region of the bolt.

**SI:** The International System of Units, an evolution of the metric sytstem.

**Strain:** With respect to bolts under tensile force, strain is the measure of elongation of the bolt as it is stretched.

**Stress:** An engineering value that is defined as force per unit area. For bolts, it is often expressed in PSI (pounds per square inch). The metric equivalent measure is MPa (megapascals).

**Stress Area:** The effective cross sectional area of the threaded region in a bolt.

**Tension:** The tensile force developed by tightening a bolt. It is equal and opposite to the clamp force – the force holding your bolted joint together. Tension is the force that SmartBolts® measure and display.

**Torque:** A twisting or rotational force given in units of pound-feet (lb-ft) or Newton-meters (Nm). It is a measure of how much force is required to turn the head or nut of a bolt. Torque is related to bolt tension by the nut factor, which is difficult to predict. SmartBolts® allow proper bolted joint installation without concern for torque or nut factor, eliminating the requirement to use a torque wrench.

**Ultimate Strength:** The maximum tensile load that a bolt can withstand before breaking.

**USCS:** The U.S. Customary System, an evolution of the British Imperial System