Calculator187 threads

Tap Drill Size Chart

The hole to drill before a tap goes in, for every thread in the database — and the reverse question a printed chart cannot answer: what will this drill in my hand actually tap?

Tap drill sizes: the hole to drill before running a tap into it. Every figure is a value stored per thread, not a rounded rule of thumb.
Thread	Standard	Pitch	Tap drill (mm)	Tap drill (in)	Detail
M1 × 0.2 fine	ISO Metric	0.200 mm	0.800	0.032	Thread data →
M1 × 0.25	ISO Metric	0.250 mm	0.750	0.029	Thread data →
M1.2 × 0.2 fine	ISO Metric	0.200 mm	1.00	0.039	Thread data →
M1.2 × 0.25	ISO Metric	0.250 mm	0.950	0.037	Thread data →
M1.4 × 0.2 fine	ISO Metric	0.200 mm	1.20	0.047	Thread data →
M1.4 × 0.3	ISO Metric	0.300 mm	1.10	0.043	Thread data →
#0-80 UNF	Unified National Fine	0.318 mm	1.21	0.048	Thread data →
M1.6 × 0.2 fine	ISO Metric	0.200 mm	1.40	0.055	Thread data →
M1.6 × 0.35	ISO Metric	0.350 mm	1.25	0.049	Thread data →
M1.8 × 0.2 fine	ISO Metric	0.200 mm	1.60	0.063	Thread data →
M1.8 × 0.35	ISO Metric	0.350 mm	1.45	0.057	Thread data →
#1-72 UNF	Unified National Fine	0.353 mm	1.50	0.059	Thread data →
#1-64 UNC	Unified National Coarse	0.397 mm	1.46	0.057	Thread data →
M2 × 0.25 fine	ISO Metric	0.250 mm	1.75	0.069	Thread data →
M2 × 0.4	ISO Metric	0.400 mm	1.60	0.063	Thread data →
#2-64 UNF	Unified National Fine	0.397 mm	1.79	0.070	Thread data →
#2-56 UNC	Unified National Coarse	0.454 mm	1.73	0.068	Thread data →
M2.2 × 0.45	ISO Metric	0.450 mm	1.75	0.069	Thread data →
M2.5 × 0.35 fine	ISO Metric	0.350 mm	2.15	0.085	Thread data →
M2.5 × 0.45	ISO Metric	0.450 mm	2.05	0.081	Thread data →
#3-56 UNF	Unified National Fine	0.454 mm	2.06	0.081	Thread data →
#3-48 UNC	Unified National Coarse	0.529 mm	1.99	0.078	Thread data →
#4-48 UNF	Unified National Fine	0.529 mm	2.32	0.091	Thread data →
#4-40 UNC	Unified National Coarse	0.635 mm	2.21	0.087	Thread data →
M3 × 0.35 fine	ISO Metric	0.350 mm	2.65	0.104	Thread data →
M3 × 0.5	ISO Metric	0.500 mm	2.50	0.098	Thread data →
#5-44 UNF	Unified National Fine	0.577 mm	2.60	0.102	Thread data →
#5-40 UNC	Unified National Coarse	0.635 mm	2.54	0.100	Thread data →
M3.5 × 0.35 fine	ISO Metric	0.350 mm	3.15	0.124	Thread data →
M3.5 × 0.6	ISO Metric	0.600 mm	2.90	0.114	Thread data →
#6-40 UNF	Unified National Fine	0.635 mm	2.87	0.113	Thread data →
#6-32 UNC	Unified National Coarse	0.794 mm	2.71	0.107	Thread data →
M4 × 0.5 fine	ISO Metric	0.500 mm	3.50	0.138	Thread data →
M4 × 0.7	ISO Metric	0.700 mm	3.30	0.130	Thread data →
#8-36 UNF	Unified National Fine	0.706 mm	3.46	0.136	Thread data →
#8-32 UNC	Unified National Coarse	0.794 mm	3.37	0.133	Thread data →
M4.5 × 0.5 fine	ISO Metric	0.500 mm	4.00	0.158	Thread data →
M4.5 × 0.75	ISO Metric	0.750 mm	3.75	0.148	Thread data →
#10-32 UNF	Unified National Fine	0.794 mm	4.03	0.159	Thread data →
#10-24 UNC	Unified National Coarse	1.06 mm	3.77	0.148	Thread data →
M5 × 0.5 fine	ISO Metric	0.500 mm	4.50	0.177	Thread data →
M5 × 0.8	ISO Metric	0.800 mm	4.20	0.165	Thread data →
#12-28 UNF	Unified National Fine	0.907 mm	4.58	0.180	Thread data →
#12-24 UNC	Unified National Coarse	1.06 mm	4.43	0.174	Thread data →
M5.5 × 0.9	ISO Metric	0.900 mm	4.60	0.181	Thread data →
M6 × 0.75 fine	ISO Metric	0.750 mm	5.25	0.207	Thread data →
M6 × 1	ISO Metric	1.00 mm	5.00	0.197	Thread data →
1/4-32 UNEF	Unified National Extra Fine	0.794 mm	5.56	0.219	Thread data →
1/4-28 UNF	Unified National Fine	0.907 mm	5.44	0.214	Thread data →
1/4-20 UNC	Unified National Coarse	1.27 mm	5.08	0.200	Thread data →
1/4-16 ACME	ACME	1.59 mm	4.76	0.188	Thread data →
M7 × 0.75 fine	ISO Metric	0.750 mm	6.25	0.246	Thread data →
M7 × 1	ISO Metric	1.00 mm	6.00	0.236	Thread data →
5/16-32 UNEF	Unified National Extra Fine	0.794 mm	7.14	0.281	Thread data →
5/16-24 UNF	Unified National Fine	1.06 mm	6.88	0.271	Thread data →
5/16-18 UNC	Unified National Coarse	1.41 mm	6.53	0.257	Thread data →
5/16-14 ACME	ACME	1.81 mm	6.12	0.241	Thread data →
M8 × 0.75 fine	ISO Metric	0.750 mm	7.25	0.285	Thread data →
M8 × 1 fine	ISO Metric	1.00 mm	7.00	0.276	Thread data →
M8 × 1.25	ISO Metric	1.25 mm	6.75	0.266	Thread data →
Tr8 × 1.5	Trapezoidal	1.50 mm	6.50	0.256	Thread data →
M9 × 1 fine	ISO Metric	1.00 mm	8.00	0.315	Thread data →
M9 × 1.25	ISO Metric	1.25 mm	7.75	0.305	Thread data →
3/8-32 UNEF	Unified National Extra Fine	0.794 mm	8.73	0.344	Thread data →
3/8-24 UNF	Unified National Fine	1.06 mm	8.47	0.333	Thread data →
3/8-16 UNC	Unified National Coarse	1.59 mm	7.94	0.313	Thread data →
3/8-12 ACME	ACME	2.12 mm	7.41	0.292	Thread data →
1/8-28 BSP	British Standard Pipe (parallel)	0.907 mm	8.82	0.347	Thread data →
M10 × 1 fine	ISO Metric	1.00 mm	9.00	0.354	Thread data →
M10 × 1.25 fine	ISO Metric	1.25 mm	8.75	0.344	Thread data →
M10 × 1.5	ISO Metric	1.50 mm	8.50	0.335	Thread data →
Tr10 × 1.5	Trapezoidal	1.50 mm	8.50	0.335	Thread data →
Tr10 × 2	Trapezoidal	2.00 mm	8.00	0.315	Thread data →
1/8-27 NPS	National Pipe Straight	0.941 mm	9.35	0.368	Thread data →
M11 × 1 fine	ISO Metric	1.00 mm	10.00	0.394	Thread data →
M11 × 1.5	ISO Metric	1.50 mm	9.50	0.374	Thread data →
7/16-28 UNEF	Unified National Extra Fine	0.907 mm	10.21	0.402	Thread data →
7/16-20 UNF	Unified National Fine	1.27 mm	9.84	0.388	Thread data →
7/16-14 UNC	Unified National Coarse	1.81 mm	9.30	0.366	Thread data →
M12 × 1.25 fine	ISO Metric	1.25 mm	10.75	0.423	Thread data →
M12 × 1.5 fine	ISO Metric	1.50 mm	10.50	0.413	Thread data →
M12 × 1.75	ISO Metric	1.75 mm	10.25	0.404	Thread data →
Tr12 × 2	Trapezoidal	2.00 mm	10.00	0.394	Thread data →
Tr12 × 3	Trapezoidal	3.00 mm	9.00	0.354	Thread data →
1/2-28 UNEF	Unified National Extra Fine	0.907 mm	11.79	0.464	Thread data →
1/2-20 UNF	Unified National Fine	1.27 mm	11.43	0.450	Thread data →
1/2-13 UNC	Unified National Coarse	1.95 mm	10.75	0.423	Thread data →
1/2-10 ACME	ACME	2.54 mm	10.16	0.400	Thread data →
1/4-19 BSP	British Standard Pipe (parallel)	1.34 mm	11.82	0.465	Thread data →
1/4-18 NPS	National Pipe Straight	1.41 mm	12.30	0.484	Thread data →
M14 × 1.5 fine	ISO Metric	1.50 mm	12.50	0.492	Thread data →
M14 × 2	ISO Metric	2.00 mm	12.00	0.472	Thread data →
Tr14 × 3	Trapezoidal	3.00 mm	11.00	0.433	Thread data →
9/16-24 UNEF	Unified National Extra Fine	1.06 mm	13.23	0.521	Thread data →
9/16-18 UNF	Unified National Fine	1.41 mm	12.88	0.507	Thread data →
9/16-12 UNC	Unified National Coarse	2.12 mm	12.17	0.479	Thread data →
5/8-24 UNEF	Unified National Extra Fine	1.06 mm	14.82	0.583	Thread data →
5/8-18 UNF	Unified National Fine	1.41 mm	14.46	0.569	Thread data →
5/8-11 UNC	Unified National Coarse	2.31 mm	13.57	0.534	Thread data →
5/8-8 ACME	ACME	3.17 mm	12.70	0.500	Thread data →
M16 × 1.5 fine	ISO Metric	1.50 mm	14.50	0.571	Thread data →
M16 × 2	ISO Metric	2.00 mm	14.00	0.551	Thread data →
Tr16 × 2	Trapezoidal	2.00 mm	14.00	0.551	Thread data →
Tr16 × 4	Trapezoidal	4.00 mm	12.00	0.472	Thread data →
3/8-19 BSP	British Standard Pipe (parallel)	1.34 mm	15.33	0.603	Thread data →
3/8-18 NPS	National Pipe Straight	1.41 mm	15.73	0.619	Thread data →
M18 × 1.5 fine	ISO Metric	1.50 mm	16.50	0.650	Thread data →
M18 × 2 fine	ISO Metric	2.00 mm	16.00	0.630	Thread data →
M18 × 2.5	ISO Metric	2.50 mm	15.50	0.610	Thread data →
Tr18 × 4	Trapezoidal	4.00 mm	14.00	0.551	Thread data →
3/4-20 UNEF	Unified National Extra Fine	1.27 mm	17.78	0.700	Thread data →
3/4-16 UNF	Unified National Fine	1.59 mm	17.46	0.688	Thread data →
3/4-10 UNC	Unified National Coarse	2.54 mm	16.51	0.650	Thread data →
3/4-6 ACME	ACME	4.23 mm	14.82	0.583	Thread data →
M20 × 1.5 fine	ISO Metric	1.50 mm	18.50	0.728	Thread data →
M20 × 2 fine	ISO Metric	2.00 mm	18.00	0.709	Thread data →
M20 × 2.5	ISO Metric	2.50 mm	17.50	0.689	Thread data →
Tr20 × 4	Trapezoidal	4.00 mm	16.00	0.630	Thread data →
1/2-14 BSP	British Standard Pipe (parallel)	1.81 mm	19.14	0.754	Thread data →
1/2-14 NPS	National Pipe Straight	1.81 mm	19.52	0.769	Thread data →
M22 × 1.5 fine	ISO Metric	1.50 mm	20.50	0.807	Thread data →
M22 × 2 fine	ISO Metric	2.00 mm	20.00	0.787	Thread data →
M22 × 2.5	ISO Metric	2.50 mm	19.50	0.768	Thread data →
7/8-20 UNEF	Unified National Extra Fine	1.27 mm	20.95	0.825	Thread data →
7/8-14 UNF	Unified National Fine	1.81 mm	20.41	0.804	Thread data →
7/8-9 UNC	Unified National Coarse	2.82 mm	19.40	0.764	Thread data →
5/8-14 BSP	British Standard Pipe (parallel)	1.81 mm	21.10	0.831	Thread data →
M24 × 2 fine	ISO Metric	2.00 mm	22.00	0.866	Thread data →
M24 × 3	ISO Metric	3.00 mm	21.00	0.827	Thread data →
Tr24 × 3	Trapezoidal	3.00 mm	21.00	0.827	Thread data →
Tr24 × 5	Trapezoidal	5.00 mm	19.00	0.748	Thread data →
1-12 UNF	Unified National Fine	2.12 mm	23.28	0.917	Thread data →
1-8 UNC	Unified National Coarse	3.17 mm	22.23	0.875	Thread data →
1-5 ACME	ACME	5.08 mm	20.32	0.800	Thread data →
3/4-14 BSP	British Standard Pipe (parallel)	1.81 mm	24.63	0.970	Thread data →
3/4-14 NPS	National Pipe Straight	1.81 mm	24.86	0.979	Thread data →
M27 × 2 fine	ISO Metric	2.00 mm	25.00	0.984	Thread data →
M27 × 3	ISO Metric	3.00 mm	24.00	0.945	Thread data →
Tr28 × 5	Trapezoidal	5.00 mm	23.00	0.905	Thread data →
1-1/8-12 UNF	Unified National Fine	2.12 mm	26.46	1.0417	Thread data →
1-1/8-7 UNC	Unified National Coarse	3.63 mm	24.95	0.982	Thread data →
M30 × 2 fine	ISO Metric	2.00 mm	28.00	1.1024	Thread data →
M30 × 3.5	ISO Metric	3.50 mm	26.50	1.0433	Thread data →
Tr30 × 6	Trapezoidal	6.00 mm	24.00	0.945	Thread data →
7/8-14 BSP	British Standard Pipe (parallel)	1.81 mm	28.39	1.1176	Thread data →
1-1/4-12 UNF	Unified National Fine	2.12 mm	29.63	1.1667	Thread data →
1-1/4-7 UNC	Unified National Coarse	3.63 mm	28.12	1.1071	Thread data →
1-1/4-5 ACME	ACME	5.08 mm	26.67	1.0500	Thread data →
M33 × 3 fine	ISO Metric	3.00 mm	30.00	1.1811	Thread data →
M33 × 3.5	ISO Metric	3.50 mm	29.50	1.1614	Thread data →
1-11 BSP	British Standard Pipe (parallel)	2.31 mm	30.94	1.2181	Thread data →
1-11.5 NPS	National Pipe Straight	2.21 mm	31.19	1.2280	Thread data →
1-3/8-6 UNC	Unified National Coarse	4.23 mm	30.69	1.2083	Thread data →
M36 × 3 fine	ISO Metric	3.00 mm	33.00	1.2992	Thread data →
M36 × 4	ISO Metric	4.00 mm	32.00	1.2598	Thread data →
Tr36 × 6	Trapezoidal	6.00 mm	30.00	1.1811	Thread data →
1-1/2-12 UNF	Unified National Fine	2.12 mm	35.98	1.4167	Thread data →
1-1/2-6 UNC	Unified National Coarse	4.23 mm	33.87	1.3333	Thread data →
1-1/2-4 ACME	ACME	6.35 mm	31.75	1.2500	Thread data →
M39 × 3 fine	ISO Metric	3.00 mm	36.00	1.4173	Thread data →
M39 × 4	ISO Metric	4.00 mm	35.00	1.3780	Thread data →
Tr40 × 7	Trapezoidal	7.00 mm	33.00	1.2992	Thread data →
1-1/4-11 BSP	British Standard Pipe (parallel)	2.31 mm	39.60	1.5591	Thread data →
M42 × 3 fine	ISO Metric	3.00 mm	39.00	1.5354	Thread data →
M42 × 4.5	ISO Metric	4.50 mm	37.50	1.4764	Thread data →
1-1/4-11.5 NPS	National Pipe Straight	2.21 mm	39.95	1.5730	Thread data →
1-3/4-5 UNC	Unified National Coarse	5.08 mm	39.37	1.5500	Thread data →
M45 × 3 fine	ISO Metric	3.00 mm	42.00	1.6535	Thread data →
M45 × 4.5	ISO Metric	4.50 mm	40.50	1.5945	Thread data →
1-1/2-11 BSP	British Standard Pipe (parallel)	2.31 mm	45.49	1.7911	Thread data →
M48 × 3 fine	ISO Metric	3.00 mm	45.00	1.7717	Thread data →
M48 × 5	ISO Metric	5.00 mm	43.00	1.6929	Thread data →
1-1/2-11.5 NPS	National Pipe Straight	2.21 mm	46.05	1.8130	Thread data →
2 UNC	Unified National Coarse	5.64 mm	45.16	1.7778	Thread data →
2-4 ACME	ACME	6.35 mm	44.45	1.7500	Thread data →
M52 × 4 fine	ISO Metric	4.00 mm	48.00	1.8898	Thread data →
M52 × 5	ISO Metric	5.00 mm	47.00	1.8504	Thread data →
M56 × 4 fine	ISO Metric	4.00 mm	52.00	2.0472	Thread data →
M56 × 5.5	ISO Metric	5.50 mm	50.50	1.9882	Thread data →
2-11 BSP	British Standard Pipe (parallel)	2.31 mm	57.30	2.2561	Thread data →
M60 × 4 fine	ISO Metric	4.00 mm	56.00	2.2047	Thread data →
M60 × 5.5	ISO Metric	5.50 mm	54.50	2.1457	Thread data →
2-11.5 NPS	National Pipe Straight	2.21 mm	58.12	2.2880	Thread data →
M64 × 4 fine	ISO Metric	4.00 mm	60.00	2.3622	Thread data →
M64 × 6	ISO Metric	6.00 mm	58.00	2.2835	Thread data →
2-1/2-8 NPS	National Pipe Straight	3.17 mm	69.85	2.7500	Thread data →
3-8 NPS	National Pipe Straight	3.17 mm	85.72	3.3750	Thread data →

Drill numbers are absent on purpose. The inch series (#1–#80, letters A–Z) is a separate table, and this database has no source for it. What is given is the diameter to 0.001 in, which is what the drill has to measure. If your drill index is stamped with a number, convert it against the manufacturer's chart rather than trusting a mapping found on a forum.

How the number is produced

nominal diameter minus pitch, and what that leaves

Thread	Major ⌀	Pitch	Tap drill	Arithmetic
M6 × 1	6 mm	1 mm	5 mm	M6 × 1: 6 − 1 = 5 mm
M8 × 1.25	8 mm	1.25 mm	6.75 mm	M8 × 1.25: 8 − 1.25 = 6.75 mm
M10 × 1.5	10 mm	1.5 mm	8.5 mm	M10 × 1.5: 10 − 1.5 = 8.5 mm
M12 × 1.75	12 mm	1.75 mm	10.25 mm	M12 × 1.75: 12 − 1.75 = 10.25 mm

1/4-20 UNC is the inch case: nominally 1/4 in (6.35 mm) at 20 TPI, and its tap drill is 5.08 mm (0.2 in) — the same subtraction done in inches. The table above the fold shows the value stored for each thread; this block shows why that value is what it is.

Frequently asked questionsengagement, clearance holes and broken taps

What size drill do I need for an M6 tap?

5 mm. That is the nominal diameter (6 mm) minus the pitch (1 mm), which leaves the standard 75%-ish thread engagement for a cutting tap. A M8 × 1.25 tap takes 6.75 mm, M10 × 1.5 takes 8.5 mm and M12 × 1.75 takes 10.25 mm.

Why is the tap drill larger than the thread's core diameter?

Because a tap has to cut, not just scrape. If the hole were exactly at the minor diameter the tap would be cutting 100% of the thread depth on every flank at once, and the torque needed to drive it would break small taps long before the thread was finished. Leaving 25% of the thread form uncut is the compromise that keeps the tap intact and still gives a thread that develops close to the full strength of the bolt.

What is the difference between a tap drill and a clearance hole?

A tap drill is the hole that gets threaded; a clearance hole is the hole the bolt passes through, and it is always larger than the bolt. On a M6 × 1 the tap drill is 5 mm while a normal clearance hole is around 6.6 mm. This page gives tap drills only — the ISO 273 clearance series is not in the database, and inventing it here would be worse than leaving it out.

Why is there no tap drill size for NPT or BSPT?

Because a tapered pipe thread is not cut with an ordinary drill. The hole is stepped — drilled, then reamed or counterbored to the taper — and the effective diameter changes along the length, so there is no single drill size that could be printed in this column. The 23 tapered threads in the database therefore have no value here, by design rather than by omission.

Is there a drill number for 1/4-20 UNC?

The database gives 5.08 mm (0.2 in) for 1/4-20 UNC. The inch drill-number series (#1–#80) and letter series (A–Z) are a separate table that this database does not carry, so no number is quoted here. Measure the drill you have: any drill within a few thousandths of 0.2 in will tap this thread.

What happens if I use a drill one size too large?

The thread engagement drops and the fastener strips sooner. For a small thread the difference is not cosmetic: going one 0.1 mm step up on an M3 removes a measurable share of the thread height, and the joint fails at lower load long before the bolt does. Going one size down is the other failure — increased tapping torque, and broken taps in blind holes where you cannot get them out.

Does this work for forming (roll) taps?

No. A forming tap displaces metal instead of cutting it, so the hole must be larger than a cutting tap's — roughly the pitch diameter of the thread rather than its minor diameter — and the figure differs by material. Every number on this page is for a cutting tap.

Why is the trapezoidal thread in this table but the pipe threads are not?

Because trapezoidal (Tr) and ACME threads are straight: they have one diameter along the whole length, so one drill size applies. The tap drill for them is the nominal diameter minus the pitch as well, and on a 30° trapezoidal thread that lands exactly on the basic minor diameter of the internal thread.

Related in the databasethe rest of the hole and the thread in it

DatabaseThread databasePitch, pitch diameter and minor diameter for every thread here DatabaseTap and dieWhat the tap is, and how it is driven without snapping DatabaseDrill bitsPoint angles and what each is for DatabaseTightening torqueWhat the finished thread will take