Radius Gauges

Radius Gauges

Radius gauges (also called fillet gauges) measure internal and external radii on machined components, castings, and finished workpieces. Where calipers measure linear dimensions and protractors measure angles, radius gauges fill the gap of measuring curves — the inside of a fillet, the outside of a corner, the radius of a turned shoulder. AIMS Industrial stocks radius gauges for engineering, inspection, and toolroom use.

The gauge types we stock

• Standard radius gauge sets — fan-handle sets containing graduated radius leaves for both internal and external radii
• Metric radius gauges — radii in millimetres, typically 0.4mm to 25mm
• Imperial radius gauges — radii in inches/fractions, typically 1/64 inch to 1 inch
• Convex/concave combination gauges — both internal and external radius readings on the same leaf
• Specialist large-radius gauges — for radii beyond the standard set range

How a radius gauge works

Each leaf in the gauge set has a precisely-formed radius profile — convex on one edge for internal radius measurement, concave on the other edge for external radius measurement. Slide the matching profile against the workpiece radius and check for full contact across the curve. If light shows between the gauge and the workpiece, the radius doesn't match the gauge; the next leaf size up or down will be closer. The right gauge sits flush with no light gap.

Where radius gauges earn their place

• Inspection — confirming machined fillets and rounds match the drawing specification
• Layout — marking the correct radius for grinding, filing, or finishing operations
• Reverse engineering — measuring the radius on an existing component to reproduce or replace it
• Quality control — checking production parts against the design radius
• Filing and finishing — guiding the work as a curve is being formed

Resolution and increment

Standard radius gauge sets typically include increments of 0.5mm at the small end (where the difference matters most for inspection) and 1mm or 2mm at the larger end. Imperial sets follow a similar pattern with 1/64 inch and 1/32 inch increments at the small end. For applications requiring intermediate radii, additional gauges can be sourced or the closest match can be used as a layout guide.

Brands stocked at AIMS

Radius gauges are stocked from quality manufacturers chosen for accurate radius forming and durable construction. Stainless steel and tool steel materials are standard; the gauge has to remain dimensionally stable under workshop conditions and survive the inevitable knocks. For specific brand requirements (Mitutoyo, Starrett-equivalent), contact our team for sourcing.

Care and accuracy

Radius gauges are precision tools that suffer from being thrown into toolboxes. Store them flat in their case or roll, keep them clean and lightly oiled to prevent rust, and inspect for damage to the leaf edges before relying on the readings. A gauge with a chipped or bent leaf reads incorrectly; replace damaged leaves rather than continuing to use them. For traceable inspection workplaces, periodic calibration may be required as part of the broader measuring tool calibration regime.

Companion ranges

Radius gauges sit alongside our broader measuring tools range — calipers, micrometers, height gauges, surface plates, dial indicators. For complete inspection setups, contact our team to discuss requirements.