Mechanical fork and micrometer thickness gauges are instruments for measuring the thickness of sheet metal, foil, film and flat materials by direct contact. They are built around a throat-shaped frame (a deep throat) that gives access even to the middle of wide products, with a fixed anvil as reference and a movable probe or a micrometer screw for the measurement. They are widespread in the machine shop, in quality control, in sheet-metal work, in the metals sector and in the metrological verification of certified thickness standards.
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Types
Fork-type thickness gauges fall into: dial gauges (with a movable probe linked to a dial indicator, resolution 0.01 mm, typical accuracy ±0.02 mm); digital gauges with a high-resolution encoder (0.001 mm) and zeroing, statistics and data-output functions; and micrometer gauges (with a micrometer screw in place of the indicator, resolution 0.001 mm, accuracy ±0.002 mm). The throat depth (overhang) ranges from 30 mm to 600 mm, and beyond for specific applications on wide sheet. There are also variants with interchangeable probes (spherical, flat, knife-edge) for special applications.
Technical characteristics
Typical measuring ranges are 0-10 mm, 0-25 mm and 0-50 mm. The contact force of the probe is calibrated and repeatable, normally 0.5-1.5 N, adjustable or fitted with a friction device to avoid deforming the workpiece. Digital models incorporate Bluetooth/USB output for automatic acquisition, GO/NOGO thresholds, statistical functions and value memory. The contact surfaces are of tungsten carbide or ceramic, for durability and stability. The geometry of the probe (spherical for measurements on flat surfaces, flat for cylindrical parts) is specific to the application.
Applications
Mechanical thickness gauges are used for the dimensional control of sheet metal and rolled metals (steel, aluminum, copper, brass), of film and thin foil (food, packaging, foil), of textiles, rubber, plastic, leather, paper and board, and of composites and technical materials. In industry they are the reference instrument for the acceptance control of raw materials and for the periodic verification of series production. For large workpieces, long-throat gauges are used; for small parts, compact workshop models are suitable.
Standards and calibration
Fork-type thickness gauges follow the technical guidelines of DIN 2103 and the ISO specifications for thickness test methods (for example ISO 4593 for plastic film, ISO 5084 for textiles). Periodic calibration uses gauge blocks and shims certified to ISO 17025. The checks cover linearity, repeatability, contact force and the flatness of the measuring surfaces. Keeping the contact surfaces clean is fundamental to consistent performance over time.
Selection criteria
Choosing the right thickness gauge means considering the measuring range, the resolution required, the throat depth needed (as a function of the size of the workpiece), the geometry of the probes (spherical, flat), the accuracy, the need for digital output for integration with quality systems, and robustness for the workshop environment. For checks on thin sheet, the 0.001 mm resolution of digital models is often indispensable; for general workshop checks, the 0.01 mm resolution of analog models is sufficient and more economical.
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