# Tap Drill Size Chart for Metric, UNC and UNF Threads

> Source: https://netray.co/tools/tap-drill-size-chart-reference
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Searchable tap drill chart for common metric coarse, metric fine, UNC and UNF sizes with the standard drill and its diameter in mm.

## Category

manufacturing

## Industry

Machining

## Audience

- CNC machinist
- CNC programmer
- Manufacturing engineer

## Tool

**Kind:** worksheet

**Mode:** reference

**Columns:**

#### Thread

**Key:** thread

**Type:** text

#### Series

**Key:** series

**Type:** text

#### Pitch / TPI

**Key:** pitch

**Type:** text

#### Major dia (mm)

**Key:** major_mm

**Type:** number

**Format:** decimal

#### Tap drill

**Key:** drill

**Type:** text

#### Drill dia (mm)

**Key:** drill_mm

**Type:** number

**Format:** decimal

**Rows:**

**Thread:** M3 x 0.5

**Series:** Metric coarse

**Pitch:** 0.5 mm

**Major mm:** 3

**Drill:** 2.5 mm

**Drill mm:** 2.5

**Thread:** M4 x 0.7

**Series:** Metric coarse

**Pitch:** 0.7 mm

**Major mm:** 4

**Drill:** 3.3 mm

**Drill mm:** 3.3

**Thread:** M5 x 0.8

**Series:** Metric coarse

**Pitch:** 0.8 mm

**Major mm:** 5

**Drill:** 4.2 mm

**Drill mm:** 4.2

**Thread:** M6 x 1

**Series:** Metric coarse

**Pitch:** 1.0 mm

**Major mm:** 6

**Drill:** 5.0 mm

**Drill mm:** 5

**Thread:** M8 x 1.25

**Series:** Metric coarse

**Pitch:** 1.25 mm

**Major mm:** 8

**Drill:** 6.8 mm

**Drill mm:** 6.8

**Thread:** M10 x 1.5

**Series:** Metric coarse

**Pitch:** 1.5 mm

**Major mm:** 10

**Drill:** 8.5 mm

**Drill mm:** 8.5

**Thread:** M12 x 1.75

**Series:** Metric coarse

**Pitch:** 1.75 mm

**Major mm:** 12

**Drill:** 10.2 mm

**Drill mm:** 10.2

**Thread:** M14 x 2

**Series:** Metric coarse

**Pitch:** 2.0 mm

**Major mm:** 14

**Drill:** 12.0 mm

**Drill mm:** 12

**Thread:** M16 x 2

**Series:** Metric coarse

**Pitch:** 2.0 mm

**Major mm:** 16

**Drill:** 14.0 mm

**Drill mm:** 14

**Thread:** M20 x 2.5

**Series:** Metric coarse

**Pitch:** 2.5 mm

**Major mm:** 20

**Drill:** 17.5 mm

**Drill mm:** 17.5

**Thread:** M24 x 3

**Series:** Metric coarse

**Pitch:** 3.0 mm

**Major mm:** 24

**Drill:** 21.0 mm

**Drill mm:** 21

**Thread:** M8 x 1

**Series:** Metric fine

**Pitch:** 1.0 mm

**Major mm:** 8

**Drill:** 7.0 mm

**Drill mm:** 7

**Thread:** M10 x 1.25

**Series:** Metric fine

**Pitch:** 1.25 mm

**Major mm:** 10

**Drill:** 8.8 mm

**Drill mm:** 8.8

**Thread:** M12 x 1.25

**Series:** Metric fine

**Pitch:** 1.25 mm

**Major mm:** 12

**Drill:** 10.8 mm

**Drill mm:** 10.8

**Thread:** M12 x 1.5

**Series:** Metric fine

**Pitch:** 1.5 mm

**Major mm:** 12

**Drill:** 10.5 mm

**Drill mm:** 10.5

**Thread:** M16 x 1.5

**Series:** Metric fine

**Pitch:** 1.5 mm

**Major mm:** 16

**Drill:** 14.5 mm

**Drill mm:** 14.5

**Thread:** M20 x 1.5

**Series:** Metric fine

**Pitch:** 1.5 mm

**Major mm:** 20

**Drill:** 18.5 mm

**Drill mm:** 18.5

**Thread:** #4-40

**Series:** UNC

**Pitch:** 40 TPI

**Major mm:** 2.845

**Drill:** #43 (0.0890 in)

**Drill mm:** 2.261

**Thread:** #6-32

**Series:** UNC

**Pitch:** 32 TPI

**Major mm:** 3.505

**Drill:** #36 (0.1065 in)

**Drill mm:** 2.705

**Thread:** #8-32

**Series:** UNC

**Pitch:** 32 TPI

**Major mm:** 4.166

**Drill:** #29 (0.1360 in)

**Drill mm:** 3.454

**Thread:** #10-24

**Series:** UNC

**Pitch:** 24 TPI

**Major mm:** 4.826

**Drill:** #25 (0.1495 in)

**Drill mm:** 3.797

**Thread:** 1/4-20

**Series:** UNC

**Pitch:** 20 TPI

**Major mm:** 6.35

**Drill:** #7 (0.2010 in)

**Drill mm:** 5.105

**Thread:** 5/16-18

**Series:** UNC

**Pitch:** 18 TPI

**Major mm:** 7.938

**Drill:** F (0.2570 in)

**Drill mm:** 6.528

**Thread:** 3/8-16

**Series:** UNC

**Pitch:** 16 TPI

**Major mm:** 9.525

**Drill:** 5/16 in (0.3125 in)

**Drill mm:** 7.938

**Thread:** 7/16-14

**Series:** UNC

**Pitch:** 14 TPI

**Major mm:** 11.113

**Drill:** U (0.3680 in)

**Drill mm:** 9.347

**Thread:** 1/2-13

**Series:** UNC

**Pitch:** 13 TPI

**Major mm:** 12.7

**Drill:** 27/64 in (0.4219 in)

**Drill mm:** 10.716

**Thread:** 9/16-12

**Series:** UNC

**Pitch:** 12 TPI

**Major mm:** 14.288

**Drill:** 31/64 in (0.4844 in)

**Drill mm:** 12.304

**Thread:** 5/8-11

**Series:** UNC

**Pitch:** 11 TPI

**Major mm:** 15.875

**Drill:** 17/32 in (0.5313 in)

**Drill mm:** 13.495

**Thread:** 3/4-10

**Series:** UNC

**Pitch:** 10 TPI

**Major mm:** 19.05

**Drill:** 21/32 in (0.6563 in)

**Drill mm:** 16.669

**Thread:** 7/8-9

**Series:** UNC

**Pitch:** 9 TPI

**Major mm:** 22.225

**Drill:** 49/64 in (0.7656 in)

**Drill mm:** 19.446

**Thread:** 1-8

**Series:** UNC

**Pitch:** 8 TPI

**Major mm:** 25.4

**Drill:** 7/8 in (0.8750 in)

**Drill mm:** 22.225

**Thread:** #10-32

**Series:** UNF

**Pitch:** 32 TPI

**Major mm:** 4.826

**Drill:** #21 (0.1590 in)

**Drill mm:** 4.039

**Thread:** 1/4-28

**Series:** UNF

**Pitch:** 28 TPI

**Major mm:** 6.35

**Drill:** #3 (0.2130 in)

**Drill mm:** 5.41

**Thread:** 5/16-24

**Series:** UNF

**Pitch:** 24 TPI

**Major mm:** 7.938

**Drill:** I (0.2720 in)

**Drill mm:** 6.909

**Thread:** 3/8-24

**Series:** UNF

**Pitch:** 24 TPI

**Major mm:** 9.525

**Drill:** Q (0.3320 in)

**Drill mm:** 8.433

**Thread:** 7/16-20

**Series:** UNF

**Pitch:** 20 TPI

**Major mm:** 11.113

**Drill:** 25/64 in (0.3906 in)

**Drill mm:** 9.922

**Thread:** 1/2-20

**Series:** UNF

**Pitch:** 20 TPI

**Major mm:** 12.7

**Drill:** 29/64 in (0.4531 in)

**Drill mm:** 11.509

**Thread:** 3/4-16

**Series:** UNF

**Pitch:** 16 TPI

**Major mm:** 19.05

**Drill:** 11/16 in (0.6875 in)

**Drill mm:** 17.463

**Notes:** Drills are the common cutting-tap choices giving roughly 65 to 75 percent thread engagement in typical steels. Forming (roll) taps need a larger drill, so use the tap maker's chart for those. Always confirm against your tap manufacturer's data and the part drawing.

## Content

**Intro:** This chart answers the question every machinist asks before a tapping operation: which drill goes under this tap. It covers common metric coarse, metric fine, UNC and UNF sizes with the drill designation and its diameter in millimetres, so you can search once and move on.

**Sections:**

#### How to use the chart

**Body:** Type the thread into the search box, for example M8, 1/4-20 or UNF, and read the tap drill from the matching row. The last column gives the drill diameter in mm, which is what most CNC tool tables and ERP tool masters want. Number and letter drills are listed with their inch size in brackets so you can check them against your drill index. Export the filtered rows to Excel or PDF to pin a copy at the machine or to load into a tooling list.

**Bullets:**

- Search by thread, series or drill name
- Use the mm column when setting up tool tables
- Export a filtered subset for a job traveller

#### Where the numbers come from

**Body:** For a 60 degree thread the tap drill is the major diameter minus the pitch times a factor tied to the thread engagement you want. Metric sizes follow the simple rule major minus pitch, which yields roughly 77 percent engagement for M10 x 1.5 with an 8.5 mm drill. Inch sizes use the nearest standard fractional, number or letter drill to the target diameter. Because drills come in fixed steps the real engagement lands within a few percent of the target, which is acceptable because 60 to 75 percent engagement gives nearly the same holding strength with far lower tapping torque.

#### Reading engagement and choosing a size

**Body:** Higher engagement means a stronger thread on paper but a much harder tap job and more tap breakage. In steel, 65 to 75 percent is the normal target. In soft aluminium or plastics a smaller drill with more engagement is fine, while in stainless, titanium and nickel alloys a slightly larger drill that reduces torque is often the better choice. If a drawing calls out a thread class and minor diameter limits, the drawing wins over any chart.

#### Common mistakes

**Body:** The most frequent error is using a metric drill for an inch thread because the sizes look close, for example 6.8 mm versus the 6.9 mm needed for 5/16-24. Another is using a cutting-tap drill with a forming tap, which produces a thread that is too tight or snaps the tap. Finally, remember that the drilled hole needs enough depth beyond the full thread length for the chamfer lead and chip space when tapping blind holes.

**Bullets:**

- Do not mix metric and inch drills
- Forming taps need a different drill
- Allow extra hole depth for the tap lead
- Check coating and hole depth in blind holes

**Cta:** If your tool masters and routings live in an ERP, we can help keep thread, drill and tap data consistent with your item and operation records.

**Faq:**

#### What size drill do I use for an M8 tap?

**Answer:** For a standard M8 x 1.25 coarse thread use a 6.8 mm drill. For the M8 x 1 fine thread use a 7.0 mm drill. Both give about 70 to 77 percent engagement with a normal cutting tap in steel and similar materials.

#### What is the tap drill for 1/4-20?

**Answer:** The usual tap drill for 1/4-20 UNC is a number 7 drill at 0.2010 inch, or 5.105 mm. For 1/4-28 UNF the usual choice is a number 3 drill at 0.2130 inch, or 5.410 mm.

#### Is this chart valid for forming taps?

**Answer:** No. Forming or roll taps displace metal instead of cutting it, so they need a larger drill, usually close to the pitch diameter. Use the chart from the tap manufacturer, because the correct size depends on the tap and the material.

#### How much thread engagement do I need?

**Answer:** Sixty to seventy-five percent is normal for steel. Beyond that, strength gain is small and tap load climbs fast. Soft materials may justify more, and tough alloys often justify less to protect the tap.

## Search terms

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