> ## Documentation Index > Fetch the complete documentation index at: https://docs.iotools.cloud/llms.txt > Use this file to discover all available pages before exploring further. # Tap Drill Size Calculator > Find the correct tap drill size for any metric or imperial thread. Pick a thread from the ISO metric coarse/fine and UNC/UNF tables (or enter a custom major diameter and pitch), set the thread engagement you want, and get the theoretical hole size plus the nearest real drill — metric, fractional, number or letter — with the engagement it actually delivers. [Try Tap Drill Size Calculator in your browser →](https://iotools.cloud/tool/tap-drill-size-calculator/) ## OpenAPI ````yaml https://api.iotools.cloud/v1/openapi post /v1/tool/tap-drill-size-calculator openapi: 3.1.0 info: title: iotools.cloud API version: 1.0.0 description: >- Run any iotools.cloud tool over HTTP. Authenticate with `Authorization: Bearer iot_live_…`. **Only `POST /v1/tool/{slug}` costs credits.** Every GET here — the catalog, a tool's schema, your balance — is free. A tool call is charged its own weight or your plan's per-call minimum, whichever is larger; `x-iotools-credit-cost` on each operation is quoted at the free-tier minimum, and `GET /v1/tools/list` returns the exact figure for your key. `GET /v1/me/credits` reports what you have left, and `GET /v1/me/usage` reports what it went on. Failures are RFC 9457 problem documents — branch on `code`. servers: - url: https://api.iotools.cloud description: Production security: - bearerAuth: [] tags: - name: Catalog description: Find a tool and read its contract. Free. - name: Converters description: >- Convert between formats, encodings, and units — Base64, CSV and JSON, timestamps, and more. Fast, free, and processed right in your browser. - name: Formatters description: >- Format, beautify, minify, and validate code and data — JSON, HTML, CSS, SQL, and regex. Clean up messy input in one click, with nothing to upload. - name: Generators description: >- Generate exactly what you need and on demand — passwords, UUIDs, QR codes, hashes, random numbers, and more. Secure, instant, and free. - name: Calculators description: >- Crunch the numbers fast — from everyday math to specialized conversions and unit work. Free online calculators that run entirely in your browser. - name: Editors description: >- Edit and transform text, code, and images with quick, focused editors that run entirely in your browser — nothing to install, and no sign-up needed. - name: Utilities description: >- Everyday developer and web utilities — DNS and IP lookups, redirect and certificate checkers, and other quick diagnostics. Free and privacy-friendly. - name: Account description: Your key's allowance, limits and usage history. paths: /v1/tool/tap-drill-size-calculator: post: tags: - Calculators summary: Tap Drill Size Calculator description: >- Find the correct tap drill size for any metric or imperial thread. Pick a thread from the ISO metric coarse/fine and UNC/UNF tables (or enter a custom major diameter and pitch), set the thread engagement you want, and get the theoretical hole size plus the nearest real drill — metric, fractional, number or letter — with the engagement it actually delivers. [Try Tap Drill Size Calculator in your browser →](https://iotools.cloud/tool/tap-drill-size-calculator/) operationId: run_tap_drill_size_calculator requestBody: required: false content: application/json: schema: type: object properties: standard: enum: - metric - imperial - custom description: Thread Standard metricThread: enum: - M1.6x0.35 - M2x0.4 - M2.5x0.45 - M3x0.5 - M3.5x0.6 - M4x0.7 - M5x0.8 - M6x1 - M8x1.25 - M10x1.5 - M12x1.75 - M14x2 - M16x2 - M18x2.5 - M20x2.5 - M22x2.5 - M24x3 - M27x3 - M30x3.5 - M33x3.5 - M36x4 - M4x0.5 - M5x0.5 - M6x0.75 - M8x1 - M10x1.25 - M10x1 - M12x1.5 - M12x1.25 - M14x1.5 - M16x1.5 - M18x1.5 - M20x1.5 - M22x1.5 - M24x2 - M27x2 - M30x2 - M33x2 - M36x3 description: Metric Thread imperialThread: enum: - '#1-64-UNC' - '#2-56-UNC' - '#3-48-UNC' - '#4-40-UNC' - '#5-40-UNC' - '#6-32-UNC' - '#8-32-UNC' - '#10-24-UNC' - '#12-24-UNC' - 1/4-20-UNC - 5/16-18-UNC - 3/8-16-UNC - 7/16-14-UNC - 1/2-13-UNC - 9/16-12-UNC - 5/8-11-UNC - 3/4-10-UNC - 7/8-9-UNC - 1-8-UNC - '#0-80-UNF' - '#1-72-UNF' - '#2-64-UNF' - '#3-56-UNF' - '#4-48-UNF' - '#5-44-UNF' - '#6-40-UNF' - '#8-36-UNF' - '#10-32-UNF' - '#12-28-UNF' - 1/4-28-UNF - 5/16-24-UNF - 3/8-24-UNF - 7/16-20-UNF - 1/2-20-UNF - 9/16-18-UNF - 5/8-18-UNF - 3/4-16-UNF - 7/8-14-UNF - 1-12-UNF description: Imperial Thread customUnit: enum: - mm - in description: Custom Thread Units majorDiameter: type: number description: Major Diameter minimum: 0 pitch: type: number description: Pitch (mm) or TPI minimum: 0 engagement: type: number description: Thread Engagement (%) minimum: 50 maximum: 100 drillSet: enum: - auto - metric - imperial description: Available Drills required: [] examples: m8_1_25_at_75: summary: M8 × 1.25 at 75% value: standard: metric metricThread: M8x1.25 engagement: '75' drillSet: auto 1_4_20_unc_at_75: summary: 1/4-20 UNC at 75% value: standard: imperial imperialThread: 1/4-20-UNC engagement: '75' drillSet: auto m10_1_5_at_65_tough_material: summary: M10 × 1.5 at 65% (tough material) value: standard: metric metricThread: M10x1.5 engagement: '65' drillSet: auto responses: '200': description: Tool output content: application/json: examples: m8_1_25_at_75: summary: M8 × 1.25 at 75% value: tool: tap-drill-size-calculator tool_version: 1.0.1 outputs: status: >- Drill 6.8 mm (0.2677 in) for M8 × 1.25 (coarse). Theoretical hole 6.782 mm at 75% engagement; this drill gives 73.9%. result: - property: Thread value: M8 × 1.25 (coarse) — Metric coarse - property: Major diameter value: 8 mm (0.315 in) - property: Pitch value: 1.25 mm - property: Target engagement value: 75 % - property: Theoretical tap drill value: 6.782 mm (0.267 in) - property: Recommended drill value: 6.8 mm - property: Drill diameter value: 6.8 mm (0.2677 in) - property: Actual engagement value: 73.9 % - property: Formula value: >- d = D − (%/100) × 1.299 × P = 8 − 0.75 × 1.299 × 1.25 alternatives: - drill: 6.5 mm mm: '6.5' in: '0.2559' engagement: 92.4 % note: High torque, tap breakage risk - drill: 6.6 mm mm: '6.6' in: '0.2598' engagement: 86.2 % note: High torque, tap breakage risk - drill: 6.7 mm mm: '6.7' in: '0.2638' engagement: 80.1 % note: High torque, tap breakage risk - drill: 6.8 mm mm: '6.8' in: '0.2677' engagement: 73.9 % note: ◄ Recommended - drill: 6.9 mm mm: '6.9' in: '0.2717' engagement: 67.7 % note: Usable - drill: 7 mm mm: '7' in: '0.2756' engagement: 61.6 % note: Usable - drill: 7.1 mm mm: '7.1' in: '0.2795' engagement: 55.4 % note: Usable credits_used: 3 credits_remaining: null 1_4_20_unc_at_75: summary: 1/4-20 UNC at 75% value: tool: tap-drill-size-calculator tool_version: 1.0.1 outputs: status: >- Drill #7 (5.105 mm) for 1/4-20 UNC. Theoretical hole 5.113 mm at 75% engagement; this drill gives 75.4%. result: - property: Thread value: 1/4-20 UNC — Unified UNC - property: Major diameter value: 6.35 mm (0.25 in) - property: Pitch value: 1.27 mm (20 TPI) - property: Target engagement value: 75 % - property: Theoretical tap drill value: 5.113 mm (0.2013 in) - property: Recommended drill value: '#7' - property: Drill diameter value: 5.105 mm (0.201 in) - property: Actual engagement value: 75.4 % - property: Formula value: >- d = D − (%/100) × 1.299 × P = 6.35 − 0.75 × 1.299 × 1.27 alternatives: - drill: '#10' mm: '4.915' in: '0.1935' engagement: 87 % note: High torque, tap breakage risk - drill: '#9' mm: '4.978' in: '0.196' engagement: 83.1 % note: High torque, tap breakage risk - drill: '#8' mm: '5.055' in: '0.199' engagement: 78.5 % note: Usable - drill: '#7' mm: '5.105' in: '0.201' engagement: 75.4 % note: ◄ Recommended - drill: 13/64" mm: '5.159' in: '0.2031' engagement: 72.2 % note: Usable - drill: '#6' mm: '5.182' in: '0.204' engagement: 70.8 % note: Usable - drill: '#5' mm: '5.22' in: '0.2055' engagement: 68.5 % note: Usable credits_used: 3 credits_remaining: null m10_1_5_at_65_tough_material: summary: M10 × 1.5 at 65% (tough material) value: tool: tap-drill-size-calculator tool_version: 1.0.1 outputs: status: >- Drill 8.7 mm (0.3425 in) for M10 × 1.5 (coarse). Theoretical hole 8.733 mm at 65% engagement; this drill gives 66.7%. result: - property: Thread value: M10 × 1.5 (coarse) — Metric coarse - property: Major diameter value: 10 mm (0.3937 in) - property: Pitch value: 1.5 mm - property: Target engagement value: 65 % - property: Theoretical tap drill value: 8.733 mm (0.3438 in) - property: Recommended drill value: 8.7 mm - property: Drill diameter value: 8.7 mm (0.3425 in) - property: Actual engagement value: 66.7 % - property: Formula value: >- d = D − (%/100) × 1.299 × P = 10 − 0.65 × 1.299 × 1.5 alternatives: - drill: 8.4 mm mm: '8.4' in: '0.3307' engagement: 82.1 % note: High torque, tap breakage risk - drill: 8.5 mm mm: '8.5' in: '0.3346' engagement: 77 % note: Usable - drill: 8.6 mm mm: '8.6' in: '0.3386' engagement: 71.9 % note: Usable - drill: 8.7 mm mm: '8.7' in: '0.3425' engagement: 66.7 % note: ◄ Recommended - drill: 8.8 mm mm: '8.8' in: '0.3465' engagement: 61.6 % note: Usable - drill: 8.9 mm mm: '8.9' in: '0.3504' engagement: 56.5 % note: Usable - drill: 9 mm mm: '9' in: '0.3543' engagement: 51.3 % note: Weak thread credits_used: 3 credits_remaining: null schema: type: object required: - tool - tool_version - outputs - credits_used - credits_remaining properties: outputs: type: object properties: status: type: string description: Recommended Drill result: type: array description: Breakdown items: type: object properties: property: type: string description: Property value: type: string description: Value x-iotools-columns: - property - value alternatives: type: array description: Nearby Drills items: type: object properties: drill: type: string description: Drill mm: type: string description: Ø (mm) in: type: string description: Ø (in) engagement: type: string description: Engagement note: type: string description: Note x-iotools-columns: - drill - mm - in - engagement - note tool: type: string description: The tool's slug, echoing the {slug} in the request path. tool_version: type: string description: Output-contract version for this tool. credits_used: type: integer description: >- Credits this call consumed, after any settlement refund. 0 when metering is disabled. credits_remaining: type: - integer - 'null' description: >- Credits left in the current monthly allowance, or null when metering is disabled. request_id: type: string description: Correlation id, also sent as x-request-id. '400': $ref: '#/components/responses/ValidationError' '401': $ref: '#/components/responses/Unauthorized' '402': $ref: '#/components/responses/InsufficientCredits' '403': $ref: '#/components/responses/ToolNotAllowed' '404': $ref: '#/components/responses/ToolNotFound' '413': $ref: '#/components/responses/PayloadTooLarge' '429': $ref: '#/components/responses/RateLimited' '500': $ref: '#/components/responses/ToolFailed' '503': $ref: '#/components/responses/ToolDisabled' security: - bearerAuth: [] components: responses: ValidationError: description: Invalid request. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/validation_error title: type: string description: Short human-readable summary of the failure. examples: - Invalid request status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - validation_error detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. fields: type: - object - string additionalProperties: type: string description: >- What failed: a map of field name → message. Absent when the body itself is malformed; a single string when the failure isn't tied to one field. example: type: https://iotools.cloud/docs/errors/validation_error title: Invalid request status: 400 code: validation_error detail: One or more inputs are invalid — see `fields`. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 fields: inputString: Required Unauthorized: description: Missing or invalid API key. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/invalid_api_key title: type: string description: Short human-readable summary of the failure. examples: - Invalid API key status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - invalid_api_key detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. example: type: https://iotools.cloud/docs/errors/invalid_api_key title: Invalid API key status: 401 code: invalid_api_key detail: 'Provide ''Authorization: Bearer ''.' request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 InsufficientCredits: description: Monthly credit allowance exhausted. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/insufficient_credits title: type: string description: Short human-readable summary of the failure. examples: - Insufficient credits status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - insufficient_credits detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. credits_used: type: integer description: Always 0 — a refused call charges nothing. credits_remaining: type: integer description: Credits left in the allowance — fewer than this call costs. example: type: https://iotools.cloud/docs/errors/insufficient_credits title: Insufficient credits status: 402 code: insufficient_credits detail: This call costs 1 credit and 0 remain in this month's allowance. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 credits_used: 0 credits_remaining: 0 ToolNotAllowed: description: Tool exists but has no API surface. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/tool_not_allowed title: type: string description: Short human-readable summary of the failure. examples: - Tool not available over the API status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - tool_not_allowed detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. example: type: https://iotools.cloud/docs/errors/tool_not_allowed title: Tool not available over the API status: 403 code: tool_not_allowed detail: >- "Background Remover" is available on iotools.cloud but has no API endpoint. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 ToolNotFound: description: No such tool. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/tool_not_found title: type: string description: Short human-readable summary of the failure. examples: - Tool not found status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - tool_not_found detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. example: type: https://iotools.cloud/docs/errors/tool_not_found title: Tool not found status: 404 code: tool_not_found detail: No tool with that slug. See GET /v1/tools/list. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 PayloadTooLarge: description: Body too large. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/payload_too_large title: type: string description: Short human-readable summary of the failure. examples: - Payload too large status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - payload_too_large detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. example: type: https://iotools.cloud/docs/errors/payload_too_large title: Payload too large status: 413 code: payload_too_large detail: Request body exceeds this tool's size limit. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 RateLimited: description: Per-minute rate limit exceeded. headers: Retry-After: description: Seconds to wait before retrying (RFC 9110 delta-seconds). schema: type: integer content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/rate_limited title: type: string description: Short human-readable summary of the failure. examples: - Rate limit exceeded status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - rate_limited detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. retry_after: type: integer description: >- Seconds until the window resets — the same value as the `Retry-After` header. example: type: https://iotools.cloud/docs/errors/rate_limited title: Rate limit exceeded status: 429 code: rate_limited detail: Too many requests. Retry in 30s. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 retry_after: 30 ToolFailed: description: Tool failed to run. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/processing_error - https://iotools.cloud/docs/errors/internal_error title: type: string description: Short human-readable summary of the failure. examples: - Tool failed to run - Internal error status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - processing_error - internal_error detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. credits_used: type: integer description: >- Always 0 on `processing_error` — a failed run is refunded, floor included. credits_remaining: type: integer description: >- Credits left after the refund. Absent when metering is disabled. example: type: https://iotools.cloud/docs/errors/processing_error title: Tool failed to run status: 500 code: processing_error detail: The tool failed to run. Please try again. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 credits_used: 0 ToolDisabled: description: Tool temporarily disabled. content: application/problem+json: schema: type: object description: >- RFC 9457 problem document, served as application/problem+json. Branch on `code`; `title` is human prose and may be reworded without notice. Some failures add extension members — `fields` on validation errors, `retry_after` on 429s, `credits_used`/`credits_remaining` on billing-adjacent failures — documented on the responses that carry them. required: - type - title - status - code properties: type: type: string format: uri description: Stable documentation URI for this failure. examples: - https://iotools.cloud/docs/errors/tool_disabled - https://iotools.cloud/docs/errors/api_unconfigured title: type: string description: Short human-readable summary of the failure. examples: - Tool temporarily disabled - API not configured status: type: integer description: HTTP status code, matching the response's own status. code: type: string description: >- Stable machine-readable error code — branch on this, not `title`. enum: - tool_disabled - api_unconfigured detail: type: string description: Human explanation of this occurrence. request_id: type: string description: Correlation id, also sent as x-request-id. example: type: https://iotools.cloud/docs/errors/tool_disabled title: Tool temporarily disabled status: 503 code: tool_disabled detail: This tool is temporarily unavailable. Try again shortly. request_id: e4042b29-8f1e-4c7a-9b52-6f0d1a3c7e11 securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: iot_live_… ````