centretocentre

Center-to-center distance, often abbreviated as center-to-center or c-to-c (sometimes written as C-C or c-c), is the straight-line distance between the centres of two features, such as holes, shafts, or mounting interfaces. It is a fundamental dimensional specification in mechanical design and fabrication, critical for ensuring proper alignment, fit, and function of assemblies.

In technical drawings, the center-to-center distance is shown as a linear dimension between two center marks. It is the Euclidean distance between the centers: in a plane, it is the straight-line distance between the two points; in three dimensions, it is the length of the segment joining the two centers.

Applications and calculations: In gear trains, the center distance between two gears with pitch diameters d1 and d2 is a = (d1 + d2) / 2, equivalently the sum of the pitch radii. In belt and pulley drives, the center distance is constrained by the belt length and the selected pulley sizes, and may be adjusted within limits to achieve proper belt tension. For mounting patterns and fixtures, c-to-c spacing determines fastener alignment and structural fit.

Tolerance and quality considerations: Center-to-center dimensions are often tightly controlled to prevent misalignment, binding, or uneven wear. Geometric dimensioning and tolerancing (GD&T) may specify true position or datum references to locate centers accurately within a given tolerance.

Limitations: The c-to-c distance specifies only the linear spacing between centers; it does not define orientation or angular relationships between features without additional constraints. See also: pitch diameter, centerline, bore spacing, mounting pattern.