Some frames have a series of numbers printed on the inside of a temple arm (the part that goes behind your ear). The first numbers are typically the manufacturer’s style number and color code. But farther down the temple arm, there may be important numbers that refer to the dimensions of the frame. These numbers are the measurement, in millimeters, of the lens width, nose bridge width, and temple arm length. Often the lens width and nose bridge width are 2-digit numbers separated by a square, and the temple arm length is a 3-digit number in front of or behind the others. Knowing these numbers can help you choose a frame similar in size when shopping.