The fineness of the filter or the aperture size is a defining characteristic for woven wire filter cloths.

Geometrick pore size is a value calculated on the basis of characteristic mesh parameters such as type of weave, wire diameter and pitch. It describes the diameter of the largest spherical beads that can pass through the mesh. The calculations on which this is based were developed and tested under laboratory conditions at Stuttgart University’s Institute for Mechanical Process Engineering within the framework of AVIF projects A224 and A251. For mesh specifications where this calculation does not apply, the pore sizes are determined using the glass bead test.

Geometric pore size is calculated without taking into account the tolerances of the structural parameters (wire diameter, distribution). Because of tight production parameters at Spoerl, the stated values are if anything underestimated. When designing a filter, it must be taken into account that geometric pore size is a true indication of particle separation through a screening action. Other separation mechanisms such as the barrier effect, diffusion and inertia will clearly also hold back smaller particles. The deposition rate is highly dependent upon the actual specification of the filter medium.