What tapping drill is commonly used for M8 × 1.25?

A 6.8 mm drill is a common starting size for an M8 × 1.25 cutting tap. Confirm the material, required thread engagement and tap manufacturer data before production.

What is the difference between metric coarse and metric fine?

Fine threads use a smaller pitch than the corresponding coarse thread diameter and therefore require a different tapping drill.

Can a cutting-tap drill chart be used for thread-forming taps?

No. Forming taps normally require a larger pre-hole. Use the forming-tap manufacturer’s specified drill size.

What information helps select a tap or cutting tool?

Provide the diameter and pitch, workpiece material, through or blind hole, machine type, existing tool reference and required quantity.

Free Engineering Reference

Tap Drill Size Chart

Search common metric coarse, metric fine, UNC, UNF, BSP, BSW, BSF and BA tapping drill sizes. Print the chart, download the Bridge Engineering reference or send a selected size straight to our quotation team.

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M3 × 0.52.5 mm drill

M6 × 1.05.0 mm drill

M8 × 1.256.8 mm drill

M10 × 1.58.5 mm drill

Metric, unified and British threads

Search Tapping Drill Sizes

Choose a thread system and search by thread, pitch, TPI or drill size. The values shown are common starting sizes for cutting taps—not guaranteed production dimensions.

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Find a thread or drill size

Metric coarse tap drill reference
Thread	Pitch	Common drill	Conversion
M1 × 0.25	0.25 mm	0.75 mm	0.0295 in
M1.2 × 0.25	0.25 mm	0.95 mm	0.0374 in
M1.4 × 0.30	0.30 mm	1.10 mm	0.0433 in
M1.6 × 0.35	0.35 mm	1.25 mm	0.0492 in
M2 × 0.40	0.40 mm	1.60 mm	0.0630 in
M2.5 × 0.45	0.45 mm	2.05 mm	0.0807 in
M3 × 0.50	0.50 mm	2.50 mm	0.0984 in
M3.5 × 0.60	0.60 mm	2.90 mm	0.1142 in
M4 × 0.70	0.70 mm	3.30 mm	0.1299 in
M4.5 × 0.75	0.75 mm	3.70 mm	0.1457 in
M5 × 0.80	0.80 mm	4.20 mm	0.1654 in
M6 × 1.00	1.00 mm	5.00 mm	0.1969 in
M7 × 1.00	1.00 mm	6.00 mm	0.2362 in
M8 × 1.25	1.25 mm	6.80 mm	0.2677 in
M10 × 1.50	1.50 mm	8.50 mm	0.3346 in
M12 × 1.75	1.75 mm	10.20 mm	0.4016 in
M14 × 2.00	2.00 mm	12.00 mm	0.4724 in
M16 × 2.00	2.00 mm	14.00 mm	0.5512 in
M18 × 2.50	2.50 mm	15.50 mm	0.6102 in
M20 × 2.50	2.50 mm	17.50 mm	0.6890 in
M22 × 2.50	2.50 mm	19.50 mm	0.7677 in
M24 × 3.00	3.00 mm	21.00 mm	0.8268 in
M27 × 3.00	3.00 mm	24.00 mm	0.9449 in
M30 × 3.50	3.50 mm	26.50 mm	1.0433 in
M33 × 3.50	3.50 mm	29.50 mm	1.1614 in
M36 × 4.00	4.00 mm	32.00 mm	1.2598 in
M42 × 4.50	4.50 mm	37.50 mm	1.4764 in
M48 × 5.00	5.00 mm	43.00 mm	1.6929 in

Metric fine tap drill reference
Thread	Pitch	Common drill	Conversion
M4 × 0.50	0.50 mm	3.50 mm	0.1378 in
M5 × 0.50	0.50 mm	4.50 mm	0.1772 in
M6 × 0.75	0.75 mm	5.20 mm	0.2047 in
M8 × 1.00	1.00 mm	7.00 mm	0.2756 in
M10 × 1.00	1.00 mm	9.00 mm	0.3543 in
M10 × 1.25	1.25 mm	8.80 mm	0.3465 in
M12 × 1.25	1.25 mm	10.80 mm	0.4252 in
M12 × 1.50	1.50 mm	10.50 mm	0.4134 in
M14 × 1.50	1.50 mm	12.50 mm	0.4921 in
M16 × 1.50	1.50 mm	14.50 mm	0.5709 in
M18 × 1.50	1.50 mm	16.50 mm	0.6496 in
M20 × 1.50	1.50 mm	18.50 mm	0.7283 in
M22 × 1.50	1.50 mm	20.50 mm	0.8071 in
M24 × 2.00	2.00 mm	22.00 mm	0.8661 in
M27 × 2.00	2.00 mm	25.00 mm	0.9843 in
M30 × 2.00	2.00 mm	28.00 mm	1.1024 in
M36 × 3.00	3.00 mm	33.00 mm	1.2992 in

UNC tap drill reference
Thread	Threads per inch	Common drill	Conversion
#4-40 UNC	40 TPI	#43	0.0890 in / 2.26 mm
#5-40 UNC	40 TPI	#38	0.1015 in / 2.58 mm
#6-32 UNC	32 TPI	#36	0.1065 in / 2.71 mm
#8-32 UNC	32 TPI	#29	0.1360 in / 3.45 mm
#10-24 UNC	24 TPI	#25	0.1495 in / 3.80 mm
#12-24 UNC	24 TPI	#16	0.1770 in / 4.50 mm
1/4-20 UNC	20 TPI	#7	0.2010 in / 5.11 mm
5/16-18 UNC	18 TPI	F	0.2570 in / 6.53 mm
3/8-16 UNC	16 TPI	5/16 in	0.3125 in / 7.94 mm
7/16-14 UNC	14 TPI	U	0.3680 in / 9.35 mm
1/2-13 UNC	13 TPI	27/64 in	0.4219 in / 10.72 mm
9/16-12 UNC	12 TPI	31/64 in	0.4844 in / 12.30 mm
5/8-11 UNC	11 TPI	17/32 in	0.5313 in / 13.49 mm
3/4-10 UNC	10 TPI	21/32 in	0.6563 in / 16.67 mm
7/8-9 UNC	9 TPI	49/64 in	0.7656 in / 19.45 mm
1-8 UNC	8 TPI	7/8 in	0.8750 in / 22.23 mm

UNF tap drill reference
Thread	Threads per inch	Common drill	Conversion
#4-48 UNF	48 TPI	#42	0.0935 in / 2.37 mm
#5-44 UNF	44 TPI	#37	0.1040 in / 2.64 mm
#6-40 UNF	40 TPI	#33	0.1130 in / 2.87 mm
#8-36 UNF	36 TPI	#29	0.1360 in / 3.45 mm
#10-32 UNF	32 TPI	#21	0.1590 in / 4.04 mm
#12-28 UNF	28 TPI	#14	0.1820 in / 4.62 mm
1/4-28 UNF	28 TPI	#3	0.2130 in / 5.41 mm
5/16-24 UNF	24 TPI	I	0.2720 in / 6.91 mm
3/8-24 UNF	24 TPI	Q	0.3320 in / 8.43 mm
7/16-20 UNF	20 TPI	25/64 in	0.3906 in / 9.92 mm
1/2-20 UNF	20 TPI	29/64 in	0.4531 in / 11.51 mm
9/16-18 UNF	18 TPI	33/64 in	0.5156 in / 13.10 mm
5/8-18 UNF	18 TPI	37/64 in	0.5781 in / 14.68 mm
3/4-16 UNF	16 TPI	11/16 in	0.6875 in / 17.46 mm
7/8-14 UNF	14 TPI	13/16 in	0.8125 in / 20.64 mm
1-12 UNF	12 TPI	59/64 in	0.9219 in / 23.42 mm

BSP (G) tap drill reference
Thread	Threads per inch	Common drill	Conversion
G 1/8-28 BSP	28 TPI	8.80 mm	0.3465 in
G 1/4-19 BSP	19 TPI	11.80 mm	0.4646 in
G 3/8-19 BSP	19 TPI	15.25 mm	0.6004 in
G 1/2-14 BSP	14 TPI	19.00 mm	0.7480 in
G 5/8-14 BSP	14 TPI	21.00 mm	0.8268 in
G 3/4-14 BSP	14 TPI	24.50 mm	0.9646 in
G 7/8-14 BSP	14 TPI	28.25 mm	1.1122 in
G 1-11 BSP	11 TPI	30.75 mm	1.2106 in
G 1 1/4-11 BSP	11 TPI	39.00 mm	1.5354 in
G 1 1/2-11 BSP	11 TPI	45.00 mm	1.7717 in
G 2-11 BSP	11 TPI	57.00 mm	2.2441 in

BSW tap drill reference
Thread	Threads per inch	Common drill	Conversion
1/8-40 BSW	40 TPI	2.55 mm	0.1004 in
3/16-24 BSW	24 TPI	3.70 mm	0.1457 in
1/4-20 BSW	20 TPI	5.10 mm	0.2008 in
5/16-18 BSW	18 TPI	6.60 mm	0.2598 in
3/8-16 BSW	16 TPI	7.90 mm	0.3110 in
7/16-14 BSW	14 TPI	9.30 mm	0.3661 in
1/2-12 BSW	12 TPI	10.50 mm	0.4134 in
5/8-11 BSW	11 TPI	13.50 mm	0.5315 in
3/4-10 BSW	10 TPI	16.50 mm	0.6496 in
7/8-9 BSW	9 TPI	19.25 mm	0.7579 in
1-8 BSW	8 TPI	22.00 mm	0.8661 in

BSF tap drill reference
Thread	Threads per inch	Common drill	Conversion
3/16-32 BSF	32 TPI	4.00 mm	0.1575 in
1/4-26 BSF	26 TPI	5.30 mm	0.2087 in
5/16-22 BSF	22 TPI	6.80 mm	0.2677 in
3/8-20 BSF	20 TPI	8.20 mm	0.3228 in
7/16-18 BSF	18 TPI	9.60 mm	0.3780 in
1/2-16 BSF	16 TPI	11.00 mm	0.4331 in
9/16-16 BSF	16 TPI	12.50 mm	0.4921 in
5/8-14 BSF	14 TPI	13.75 mm	0.5413 in
3/4-12 BSF	12 TPI	16.50 mm	0.6496 in
7/8-11 BSF	11 TPI	19.50 mm	0.7677 in
1-10 BSF	10 TPI	22.25 mm	0.8760 in

BA tap drill reference
Thread	Pitch	Common drill	Conversion
0 BA	1.00 mm	5.00 mm	0.1969 in
1 BA	0.90 mm	4.40 mm	0.1732 in
2 BA	0.81 mm	3.90 mm	0.1535 in
3 BA	0.73 mm	3.40 mm	0.1339 in
4 BA	0.66 mm	2.95 mm	0.1161 in
5 BA	0.59 mm	2.65 mm	0.1043 in
6 BA	0.53 mm	2.30 mm	0.0906 in
7 BA	0.48 mm	2.05 mm	0.0807 in
8 BA	0.43 mm	1.80 mm	0.0709 in
9 BA	0.39 mm	1.55 mm	0.0610 in
10 BA	0.35 mm	1.40 mm	0.0551 in

Important selection note

These are common cutting-tap starting sizes. Required pre-hole size varies with thread tolerance, percentage engagement, tap geometry and workpiece material. Thread-forming taps require different, normally larger, pre-holes. Always confirm the current tap manufacturer’s data before production or safety-critical use.

Guided selection aid

Which Type of Tap Do I Need?

Answer four questions to create a practical starting specification for Bridge Engineering to verify and quote.

Workpiece material Hole type Method Thread system Thread size or existing reference

Practical tapping guidance

Choosing the Right Tap

Spiral-point taps

Commonly used for machine tapping through holes because chips are driven forward out of the hole.

Spiral-flute taps

Often selected for blind holes because the flutes draw chips back towards the hole entrance.

Hand tap sets

Taper, second and bottoming taps provide progressive manual threading where machine tapping is unsuitable.

Thread-forming taps

Produce threads without chips in suitable ductile materials, but require a manufacturer-specified larger pre-hole.

Need the Matching Tap and Drill?

Bridge Engineering can source Dormer Pramet and other leading cutting-tool ranges for workshop and production requirements.