The same rack may contain four naming systems. A clear setup sheet records both the designation and decimal diameter to reduce selection errors.
Common mistakes
#7 does not mean 7/64 inch. Letter F is a size designation, not a tolerance grade. A metric value converted to inches may not match a stock inch drill exactly.
- Read the package and shank marking.
- Verify questionable tools with a drill gauge or suitable measurement.
- Return tools to labeled storage after use.
Compare on one basis
Decimal inches provide a convenient common column for the traditional U.S. systems; millimeters work equally well when conversion uses the exact inch definition.
Important limitation
Measuring flute lands with handheld calipers can be misleading. Use proper metrology when tool diameter must be established accurately.
Measuring flute lands with handheld calipers can be misleading. Use proper metrology when tool diameter must be established accurately.