Frames are described by three numbers stamped on the temple: eye size (lens width), bridge width and temple length in millimetres, for example 52-18-140. These follow the boxing system defined in ISO 8624. ISO 12870 sets requirements for frame quality: dimensional stability, endurance, nickel release, resistance to sweat and optical radiation.
Fit depends on more than the three numbers: frame front width, pantoscopic tilt, wrap angle and nose pad type all matter, and Asian-fit frames use lower bridges and different pad positions. Children's frames need smaller sizes and softer materials.
For OEM production the tech pack should give full dimensions, materials, colours (with acetate or plating references), hinge type, lens shape file, markings and packaging, plus the standards to test against. Samples should be checked against the tech pack before bulk.