Letter drill bit sizes
Letter sizes A–Z fill gaps above many number sizes — the stamps you see on denser jobber sets and tap charts. Each row lists the letter, decimal inch, and millimeter equivalent so you can match a drawing without opening the full four-system chart. Need fractional, metric, or number? Use the links below or the flagship chart.
Full size chart · Size finder · Drill hub · Fractional · Metric · Number
How to use this table
Scan the Size column for the letter stamp on the bit or the letter on a tap-drill chart. Decimal inch and mm are nominal workshop values. Click Find on a row to open the size finder with that label preselected — kit matching stays on the tool page. Wave0 hub chips promote mapped fractional staples only; letter sizes often default-fallback with an honest note when the lid map does not list them.
Letters increase in diameter from A toward Z (opposite the number-gauge intuition). If 1/4" is slightly tight and you need a few thousandths more, letter F is a common neighbor — always confirm with decimal columns rather than memory. For screw clearance versus pilot, diameter alone still does not choose thread engagement; pair with a screw→drill workflow when you have one.
Typical flow: read the letter from the chart or stamp, find the row, note mm if you hold a metric box, then Find → size finder. This split stays a quiet reference; the flagship chart and finder own navigation and commerce. Critical fits need a gauge. Do not treat every row as a buy button.
Coverage is the verified letter anchors in our dual-sourced data (status=ok), not a promise that every A–Z industrial step is already published. Additional letters can expand later without changing Find behavior. We never advertise an unmapped letter on hub money CTAs as if the default consumer set includes it on the lid. Keep this page for identification and cross-check; open the finder only when you actually need kit context for a label.
FAQ
What are letter drill bit sizes?
Letter sizes run A through Z and sit above many number sizes in diameter. They fill gaps that fractional steps skip, especially in metalworking and tap-drill charts.
Is every letter A–Z on this page?
This page lists the verified letter rows in our current dual-sourced table (common anchors across the alphabet, not a claim that every letter is already published). Rows shown are status-ok reference data. Additional letters can ship in later data waves.
How do letter sizes compare to fractional bits?
Use the decimal-inch and mm columns. Example: letter F is about 0.2570" — slightly larger than 1/4" (0.2500"). Pick letter when a fraction is slightly undersize for the hole you need.
Can I buy a kit from this page?
No product grid here. Click Find on a row to open the size finder. Letter labels are often outside Wave0 fractional kit maps; the card may show a default set with an honest note when the size is not mapped.
Sources
Letter diameters follow common published letter-drill indexes used in workshop references. Values are nominal. Confirm critical fits on the bit or with a gauge. See the site disclaimer for limits of use.