What Is an Aperture? Definition, Measurement & Role in Vibratory Screening

An aperture is the clear opening between adjacent wires in a woven wire screen, measured as the distance from the inside edge of one wire to the inside edge of the next wire. In vibratory screening, the aperture defines the cut point — the maximum particle size that can pass through the screen. Particles smaller than the aperture fall through as undersize (fines), while particles larger than the aperture are retained and discharged as oversize (tails).

Aperture is the physical reality behind the mesh size number. While mesh size counts openings per linear inch, the aperture tells you exactly how large each opening is in microns, millimeters, or inches. This distinction is important because two screens with the same mesh count can have different apertures if they use different wire diameters. When product specifications demand a precise particle size cutoff, the aperture — not the mesh count — is the specification that matters.

Aperture, Mesh Size, and Wire Diameter — How They Relate

For a woven wire screen, aperture is determined by this relationship:

Aperture = (1 / Mesh Count) - Wire Diameter

Expressed in inches, for a 1-inch span: if a 100 mesh screen uses wires of 0.0041" diameter, the aperture is (1/100) - 0.0041 = 0.0059" (approximately 149 microns). Changing the wire diameter changes the aperture even though the mesh count stays the same.

As the table shows, switching from standard to light wire on a 100 mesh screen increases the aperture from 149 μm to 163 μm — a 9% change. For applications where the cut point must be exact, specifying the aperture in microns is more reliable than specifying mesh size alone.

Aperture Shapes in Vibratory Screening

Woven wire screens can be manufactured with different aperture shapes, each suited to specific materials and applications:

The vast majority of round vibratory separators made by Sweco, Kason, Midwestern Industries, Cleveland Vibratory, Russell Finex, and ScreenerKing use square-aperture woven wire mesh. Rectangular and slotted apertures are more common on linear and rectangular vibratory screeners used in high-capacity or specialized dewatering applications.

Why Aperture Matters in Vibratory Screening

• Defines the cut point — The aperture is the dividing line between oversize and undersize material. Every particle in your process is classified relative to the screen aperture.
• Controls product specification compliance — When a quality specification says "100% below 150 microns," the aperture must be sized to guarantee compliance — typically set slightly below the maximum allowed particle size to account for aperture tolerances and near-size particles that pass through at an angle.
• Determines open area percentage — Aperture size, together with wire diameter, determines how much of the screen surface is open space, which directly affects throughput.
• Influences blinding risk — When a significant fraction of the feed material is close to the aperture size (near-size particles), blinding risk increases because particles become wedged in the openings.

Related Glossary Terms

• Mesh Size — The openings-per-inch count that, with wire diameter, determines aperture
• Micron — The unit most commonly used to express aperture size on fine screens
• Wire Diameter — The thickness of the screen wire that directly affects aperture for a given mesh count
• Open Area Percentage — The ratio of total aperture area to total screen area
• Blinding — Clogging caused by near-size particles lodging in apertures
• Oversize / Overs / Tails — Material retained on the screen (larger than the aperture)

Aperture FAQs

What is an aperture on a vibratory screen?

An aperture is the clear open space between two adjacent wires in a woven wire screen. It is measured as the distance from the inside edge of one wire to the inside edge of the neighboring wire. The aperture defines the cut point of the screen — particles smaller than the aperture pass through as undersize, while particles larger than the aperture are retained as oversize.

How is aperture different from mesh size?

Mesh size counts the number of openings per linear inch, while aperture measures the actual size of each individual opening. Two screens can have the same mesh count but different aperture sizes if they use different wire diameters. Aperture is the more precise specification because it directly tells you the opening dimension, whereas mesh size requires you to also know the wire diameter to determine the actual opening.

What units are used to measure screen aperture?

Screen aperture is measured in microns (μm), millimeters (mm), or inches, depending on the industry and region. Microns are the most common unit for fine screening applications (below 1 mm), while millimeters or inches are used for coarser screens. In North America, mesh size is often used as a shorthand, but the aperture in microns or millimeters is the precise physical measurement.