Every answer carries
its uncertainty.

The number series (#80–#1) and letter series (A–Z) are stored as nominal decimal-inch values and cross-checked against public OSG and Guhring manufacturer charts. The ASME B94.11M standard page establishes the subject, but the full standard text is paywalled.

Fractional sizes are generated as exact 1/64-inch increments through 1 inch and reduced for display. The metric comparison list is generated from 0.5 through 13.0 mm at 0.1 mm increments. That list does not claim every size appears in a commercial drill index.

d = D − e × 1.299038106 × P

D is nominal major diameter, P is pitch, and e is the requested theoretical full-thread fraction. This follows the basic 60° profile and is useful for comparing nominal cutting-tap targets. It does not select a tolerance class or model tap geometry, runout, material recovery, actual hole size, torque, or strength.

At 50%, the equation lands on the basic pitch-diameter relationship. At approximately 83.3%, it lands on the basic internal minor-diameter reference. That 83.3% point is a geometric reference—not a universal practical interference threshold. “100%” is only the equation’s theoretical sharp-V limit and is not used as a manufacturing claim.

Forming taps, NPT/pipe, STI, ACME, Whitworth, and other profiles are excluded. A published row means its discrete bit matched a named 65% or 75% Guhring column. Other familiar rows remain visibly provisional until row-level reconciliation is complete.

The advisor is restricted to seven traditional ANSI/ASME B18.6.1 number sizes whose shank and root diameters were transcribed from AWC NDS 2018 Appendix L, Table L3. Chapter 12 sections 12.1.5.2–12.1.5.3 provide the lead-hole ratios by withdrawal/lateral loading and wood specific gravity.

• Withdrawal: 90% of root diameter for G > 0.6; 70% for 0.5 < G ≤ 0.6; no lead hole required by that specific rule for G ≤ 0.5.
• Lateral: approximately shank/root diameter in the respective members for G > 0.6; approximately 7/8 of each for G ≤ 0.6.

Those installation provisions do not create a universal modern-screw table. Structural, deck, cabinet, self-drilling, and proprietary screws are explicitly routed to their current manufacturer instructions.

Calibration uses the 53.98 mm short edge of an ISO/IEC 7810 ID-1 card. Two independent passes are averaged; their disagreement contributes to the uncertainty band. The tool also imposes a 0.15 mm minimum uncertainty floor and invalidates calibration when viewport, orientation, device pixel ratio, or visual zoom changes.

Every nominal drill within that band is returned as a candidate group. The interface never claims that a screen comparison uniquely identifies close number, letter, fraction, or metric sizes. A drill gauge or caliper remains the final check.