Bultcirkel

Bultcirkel is a term used in mechanical engineering to refer to the bolt circle, or pitch circle diameter (PCD), of a bolt pattern. It is the imaginary circle that passes through the centers of all mounting holes on a flange, wheel, brake rotor, or similar component. The diameter of this circle is called the bolt circle diameter (D or PCD).

The bolt circle defines compatibility between mating parts. When two components are joined by bolts, they must share the same bolt circle diameter and the same number of bolts to align correctly. This concept is common in automotive wheels, hub assemblies, brake discs, flanges, sprockets, and other bolted interfaces.

Specification and measurement: Bolt patterns are described by two values: the number of bolt holes n and the bolt circle diameter D. For example, a 5x114.3 pattern means five holes evenly spaced on a circle with a diameter of 114.3 millimeters. In evenly spaced patterns, hole centers lie on a circle of radius R = D/2, with angular spacing of 360/n degrees. If holes are not perfectly evenly spaced, the term PCD still refers to the circle that best fits the centers, and D is the fitted diameter. Measurement is typically done with calipers or hole-layout tools, and tolerances depend on industry standards and the specific application.

Variations exist in units: PCD is commonly given in millimeters in metric systems, or in inches in imperial systems. The bolt circle concept is a foundational standard in parts interchangeability and mechanical design, ensuring that components can be securely and accurately joined.