Manufacturing & Production Glossary

The initial tension force in a bolt created during tightening. Preload clamps joint members together and must be sufficient to prevent joint separation under service loads while staying below bolt yield strength.

A dimensionless coefficient relating applied torque to achieved bolt preload in the equation T = K × D × F. It accounts for friction in threads and under the bolt head or nut bearing surface.

The maximum load a fastener can withstand without permanent deformation. It is typically 85-95% of yield strength and represents the practical upper limit for bolt preload.

Mass per unit volume of a material, typically expressed in kg/m³ or lb/ft³. A fundamental property used in weight calculations and fluid mechanics.

A triangular cross-section weld joining two surfaces at approximately right angles. The most common weld type, used for lap joints, T-joints, and corner joints. Specified by leg size.

The shortest distance from the root of a weld to its face, which determines weld strength. For equal-leg fillet welds, throat = 0.707 × leg size. Stress is calculated based on throat area.

The maximum stress permitted in a weld, determined by electrode strength and safety factors. Per AWS D1.1, fillet weld allowable shear = 0.30 × electrode tensile strength (Fexx).

A measure of process potential capability, calculated as Cp = (USL - LSL) / (6σ). It compares the specification width to the process spread, assuming the process is centered. Cp only measures spread, not centering.

The key measure of actual process capability, calculated as Cpk = min(Cpl, Cpu) where Cpl = (Mean - LSL)/(3σ) and Cpu = (USL - Mean)/(3σ). Unlike Cp, Cpk accounts for process centering.

A quality methodology targeting 3.4 defects per million opportunities (DPMO). The name refers to having 6 standard deviations between the process mean and specification limits. Cpk = 2.0 represents Six Sigma capability.

A measure of defect rate expressed as defective units per million produced. Calculated from the probability of measurements falling outside specification limits under normal distribution assumptions.

The largest diameter of a screw thread, measured at the crest (top) of the external thread or the root of the internal thread. This is the nominal size of the screw (e.g., a #6 screw has 0.138" major diameter).

The smallest diameter of a screw thread, measured at the root (bottom) of the external thread or the crest of the internal thread. This dimension is critical for thread strength calculations.

The distance between adjacent thread crests, measured parallel to the thread axis. In metric threads, pitch is expressed in millimeters. In imperial threads, pitch is the reciprocal of threads per inch (TPI).

The recommended drill size for creating a hole before tapping internal threads. The tap drill size is slightly larger than the minor diameter to allow for thread cutting and chip clearance.

The distance between two parallel flat surfaces of a hex bolt head or nut, measured perpendicular to the axis. This dimension determines the wrench size needed to tighten the fastener.