Wire cloth with square openings is specified by aperture size and wire diameter. The aperture size (w) describes the distance between to neighbouring warp or weft wires, measured in the centre of the aperture.  The wire diameter (d) given in the specification always refers to the measurement taken before weaving.  The weaving process may have a slight effect on the wire diameter.  Pitch (t) consists of the sum of the aperture size and the wire diameter: t = w + d.