PCD (Pitch Circle Diameter), also known as bolt pattern or screw pattern, refers to the geometric arrangement of the mounting holes in the rim or rim of a wheel. It is a critical parameter when selecting new wheels or fitting custom wheels to a vehicle, as the PCD must match that of the vehicle's wheel hub for a proper fit.

PCD is measured in millimeters and is determined by measuring the distance between the centers of two opposing mounting holes in the wheel. In most cases, vehicles have a specific PCD, which can be 4, 5, 6, 8 or more bolts. Some common examples are PCD 4x100 (4 bolts), PCD 5x114.3 (5 bolts), or PCD 6x139.7 (6 bolts).

When changing wheels on a vehicle or choosing custom wheels, it is essential to ensure that the PCD of the new wheels exactly matches the PCD of the vehicle's wheel hub. Otherwise, the mounting holes will not align properly and the wheels will not mount securely and accurately to the vehicle.

It is important to note that in addition to PCD, center diameter (the size of the hole in the center of the wheel) and offset should also be considered when selecting new wheels for a vehicle.

Wheels with the incorrect PCD can cause mounting problems, wheel imbalance, vibrations and uneven tire wear, negatively affecting vehicle performance, safety and stability. Therefore, it is always essential to carefully check the proper PCD before purchasing new or custom wheels to ensure a precise and secure fit on the vehicle.