570 records

What drill size do I need to tap this thread, and what is its decimal-inch size?

570 records covering 519 thread or drill designations, one fact each. Every value is transcribed from the source that states it and carries the sentence it was taken from: 4 sources across 2 sites, last checked 2026-11-03, due for re-check by 2031-08-27. Every record has a page of its own, quoting the line that states it.

Cite as: Tap drill size and drill-size decimal equivalents, referencesource.org/drill-tap-decimal-equivalents/, checked 2026-11-03.

6 records where two or more sources state different values. Both sides are reproduced on the record page, each with its own source and quote.

About this data

Two related lookups machinists and hobbyists need together: (1) which tap drill to use for a given inch or metric thread (e.g. 1/4-20 UNC needs a #7 drill for approximately 75% thread engagement), and (2) the decimal-inch size of every number, letter, fraction and metric drill, so a shop can pick the nearest drill it actually owns. Two independent vendor sources are used for each table so a disagreement between them can be flagged rather than silently trusted. Answers 'what size do I drill before tapping 1/4-20', and 'what decimal is a #7 drill' — a complete range in one place beats looking up one size at a time.

The data

Showing the first 400 of 570 records. Every record has its own page, with its source and the quoted line that states it; these list the rest.

• Records 1–4000.35 mm … 27/32"
• Records 401–57027/64" … Z

Where this came from

Every record above links the page it was taken from and quotes the sentence that states it. These are the 4 sources this dataset was assembled from.

• newmantools.comhttp://newmantools.com/decinch.htm
• victornet.comhttps://www.victornet.com/reference/Sizes_Equivalents.html
• newmantools.comhttps://www.newmantools.com/tapdrill.htm
• victornet.comhttps://www.victornet.com/reference/Tap_Drill.html

Machine-readable

• data.jsonThe whole dataset — every record with its source URL and source quote.
• Open Knowledge Format bundleOne JSON object per line — every record's frontmatter and quoted span exactly as it is held here, in one fetch.
• data.csvThe same records as one flat table, for a spreadsheet or a dataframe. The last four columns are the source URL, the quoted sentence it was read from, the date we last checked it, and which columns are our reading rather than the page's words.
• How this is made and checkedWhat "verified against source" does and does not mean.

From your own code

Same records, same quotes, without scraping the page: refsource is on PyPI and npm. Each value comes back carrying the URL it was read from and the sentence on that page that states it — .source and .quote sit on the value itself rather than in a side channel, so the checking step is available instead of skipped.

pip install refsource
refsource lookup drill-tap-decimal-equivalents thread_or_drill_size="0.35 mm"

npx -y refsource lookup drill-tap-decimal-equivalents thread_or_drill_size="0.35 mm"

Set your AI assistant up to use this

Two files and no account. Put this in .mcp.json at the root of your project — Claude Code, Cursor, Windsurf, VS Code and Codex all read that file — and your assistant can look this dataset up instead of recalling it. The server is remote, keyless and read-only.

{
  "mcpServers": {
    "referencesource": {
      "type": "http",
      "url": "https://referencesource.org/mcp"
    }
  }
}

Add to Cursor · or, on the command line: claude mcp add --transport http referencesource https://referencesource.org/mcp --scope project

Then one line in the project's CLAUDE.md or AGENTS.md, so the assistant knows when to reach for it:

When a question needs "Tap drill size and drill-size decimal equivalents", call the referencesource MCP server at https://referencesource.org/mcp (tool `search_records`, dataset_slug `drill-tap-decimal-equivalents`) instead of answering from memory — every record it returns carries its source URL and a verbatim quote from that page.

What each tool does, and the servers built over single registers: Connect your AI assistant.

570 records. last verified against source 2026-11-03. due for re-check by 2031-08-27.

Licence. Factual compilation with source citations. Tap drill sizes and drill decimal equivalents are standard machining facts (ANSI/ASME B1.1 practice), not the vendor's original expression; short attributed quotes link back to the published table.