Smart Drill Size Finder - Fractional, Number, Letter & Metric Cross-Reference

How It Works

1. Enter a Supported Drill Size

   Type a fractional, number, letter, metric, or decimal-inch size supported by the local parser.

2. View Decimal Equivalents

   See the nominal drill diameter in decimal inches and millimeters.

3. Check Nearest Local Rows

   Review the nearest generated fractional, number, letter, and metric rows with nominal deviations.

4. Review Neighbors Table

   See nearby nominal rows sorted by decimal diameter.

5. Treat Tap Rows as Caveats

   Tap-drill rows are common shop references and still need thread class, material, tap style, and gaging validation.

Built For

• Machinists converting between number, letter, fractional, and metric drill sizes
• CNC programmers looking up decimal equivalents for drill call-outs on older drawings
• Tool crib operators identifying unlabeled drills by measured diameter
• Maintenance mechanics finding substitute drill sizes from available inventory
• Engineering students learning the four drill size systems
• Purchasing agents cross-referencing drill sizes across suppliers

Features & Capabilities

Supported Input Parser

Auto-detects common fractional, number, letter, metric, and decimal-inch entries within the local parser scope.

391 Local Drill Rows

#1-#60 number rows, A-Z letter rows, 1/64 inch through 1 inch fractional rows, and 1.0-25.0 mm metric rows.

Neighbors Table

Shows nearby nominal rows sorted by decimal diameter across the generated local table.

Tap Drill Caveats

Flags 27 common tap-drill rows while warning that thread class, material, tap style, and gaging can change the required hole size.

Filterable Chart

Browse the generated local rows by system, name, inch value, or millimeter value.

PDF Export

Export results with source warnings and assumptions for toolbox reference or review.

Assumptions

• Fractional drill sizes are generated in 1/64-inch increments from 1/64 to 1 inch.
• Number drill sizes cover #1 through #60.
• Letter drill sizes cover A through Z.
• Metric drill sizes are generated in 0.1mm increments from 1.0mm to 25.0mm.
• Nearest-match algorithm finds the drill with smallest absolute deviation from the target diameter
• Tap drill cross-reference uses local common-shop rows and does not determine final thread percentage or acceptance.

Limitations

• Actual drill diameters vary by manufacturer tolerance class, tool condition, coating, and measurement method.
• Worn or resharpened drills may cut oversize by 0.001-0.005 inches beyond nominal
• Local generated rows are not a complete standards table and do not prove supplier availability.
• Does not include spade drill, indexable drill, or specialized core drill sizes
• Sub-millimeter metric drills (below 1mm) may not be available from all suppliers
• Tap drill recommendations are for cutting taps only; form taps require different pilot hole sizes

References

• ASME B94.11M - Twist Drills source page.
• ASME B1.1 - Unified Inch Screw Threads source page.
• ISO 2306 - Drills for use prior to tapping screw threads source page.
• ASME B1.13M - Metric Screw Threads source page.
• Current manufacturer, supplier, drawing, and gaging requirements for final acceptance.

Frequently Asked Questions