Most pins are described by two numbers. Take for example 26 mm x 0.50 mm The first number "26" describes the length of the pin in millimetres. A 26 pin is approximately 2,6 cm long. The higher this number the longer the pin. The lower this number the shorter the pin.
The second number "0.50" describes the diameter of the pin (in hundredths of a millimeter). The higher the number the thicker the pin.
The lower the number, the thinner the pin