A wheel size is written as diameter x width, followed by the bolt pattern, offset and centre bore. For example: 7Jx16H2 5/120 ET47 66.6.
Reading the stamp
The number before the letter is the rim width in inches, measured between the bead seats. The letter (J, JJ or K) describes the bead-seat profile. The number after it is the diameter in inches, measured at the bead seat rather than the outer lip.
Bolt pattern (PCD)
Written as the number of studs followed by the pitch circle diameter in millimetres. A 5×114.3 pattern has five studs on a 114.3 mm circle. This must match your hub exactly or the wheel will not mount.
Offset (ET)
Offset is the distance in millimetres from the mounting surface to the true centreline of the wheel. Positive offset pushes the wheel inward, negative offset pushes it outward. A mismatch causes rubbing, changes steering feel and loads the suspension bearings. Most manufacturers allow a tolerance of a few millimetres.
Centre bore
The hub opening, in millimetres. It must be at least as large as the hub pilot bore. A centre bore that is too small needs an adapter; one that is too large may need a hub-centric ring.
Load rating
Stamped as the maximum load in kilograms or pounds. Check it against your vehicle weight per axle, especially for SUVs, pickups and commercial applications.