Measuring the Tolerance of a Drilled Hole

The best methods for measuring the tolerance of a drilled hole depend on your precision requirements and available equipment. Here are the most effective approaches:

Basic Methods

• Go/No-Go Gauges: Simple cylindrical pins calibrated to the minimum and maximum allowable hole diameters. If the "go" pin fits and the "no-go" pin doesn't, the hole is within tolerance.
• Pin Gauges: Sets of precisely machined pins with small diameter increments that determine hole size by finding which pins fit.

Precision Methods

• Inside Micrometers: For holes typically larger than 0.5 inches, providing measurements with precision to 0.001" or better.
• Bore Gauges: For accurate measurement of hole diameter, with digital versions offering precision to 0.0001".
• Coordinate Measuring Machine (CMM): For highest precision and comprehensive measurement of diameter, roundness, cylindricity, and position.

Digital Methods

• Digital Calipers: For basic measurement of accessible holes.
  
• Digital Bore Gauges: Electronic versions of traditional bore gauges with digital readouts.
  
• Optical Comparators: For measuring profile accuracy of holes.

For most production environments, go/no-go gauges are the cheapest and simplest operation for rapid inspection and bore gauges or CMMs for detailed measurements when higher precision is required.