List of drill and tap sizes explained

Below is a comprehensive drill and tap size chart for all drills and taps, imperial and metric, up to 36.5mm in diameter.

In manufactured parts, holes with female screw threads are often needed; they accept male screws to facilitate the building and fastening of a finished assembly. One of the most common ways to produce such threaded holes is to drill a hole of appropriate size with a drill bit and then tap it with a tap. Each standard size of female screw thread has one or several corresponding drill bit sizes that are within the range of appropriate size—slightly larger than the minor diameter of the mating male thread, but smaller than its pitch and major diameters. Such an appropriately sized drill is called a tap drill for that size of thread, because it is a correct drill to be followed by the tap. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%. Usually thread depths of 60% to 75% are desired.

People frequently use a chart such as this to determine the proper tap drill for a certain thread size or the proper tap for an existing hole.

Rules of thumb

Regarding the proportion of tap drill to thread major diameter, for standard V threads (ISO V thread and UTS V thread), there are several rules of thumb with strong predictive power:

• A good tap drill is 85% (± 2 pp) of major diameter for coarse threads, and 90% (± 2 pp) of major diameter for fine threads. ^[1]
• For metric V threads, the concept of major minus pitch (i.e., the major or widest diameter of the intended screw in millimeters minus the pitch of the threads of that screw in millimeters per thread) yields a good tap drill diameter. The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20in (20 threads per inch) has a pitch of 0.050in and a in pitch (13 threads per inch) has a pitch of 0.077in. Your result will only land near a tap drill size (not directly on one).
• For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the only possible one, but it is a good one for general use.
• The 85% and 90% rules works best in the range of NaNinches–1inchesin (–in), the sizes most important on many shop floors. Some sizes outside that range have different ratios.

Below, these guidelines are explored with examples.

Examples

• • Example (inch, coarse): For size (this is the diameter of the intended screw in fraction form)-14 (this is the number of threads per inch; 14 is considered coarse), 0.437in × 0.85 = 0.371in. Therefore, a size screw (≈ 0.437) with 14 threads per inch (coarse) needs a tap drill with a diameter of about 0.371 inches.
    • The drill sizes that are near this are letter U (0.368in; 84.2%), 9.5 mm (0.374in; 85.6%), and in (0.375in; 85.8%); any of these will work well.
  • Example (inch, fine): For -20 (same diameter as the previous example, but this time with 20 threads per inch, which is considered fine), 0.437in × 0.90 = 0.393in (i.e., if the threads are to be fine, then a slightly larger diameter drill bit should be used before tapping the hole for the screw).
    • The drill sizes that are near this are (0.391in; 89.4%), 10 mm (0.393in; 90%), and letter X (0.397in; 90.8%); any of these will work well.
  • Example (metric, coarse): For M7.0×1.0 (an intended screw with a diameter of 7.0 mm and a pitch of 1 mm between each thread, which is considered coarse), 7.0mm × 0.85 = 5.95mm.
    • The drill sizes that are near this are in (85%), 6.0 mm (85.7%), and 6.1 mm (87.1%); any of these will work well.
  • Example (metric, fine): For M7.0×0.5, 7.0mm × 0.90 = 6.30.
    • The drill sizes that are near this are 6.3 mm (90%), in (90.7%), 6.4 mm (91.4%), and 6.5 mm (92.9%); any of these will work well.
• For metric V threads, major minus pitch yields a good tap drill diameter.
  • Example (metric, coarse): For M7.0 × 1.0, 7.0 − 1.0 = 6.0
  • Example (metric, fine): For M7.0 × 0.5, 7.0 − 0.5 = 6.5
    • (The 85% coarse, 90% fine guideline, within its effective range, matches this in net effect)
  • The major minus pitch also works for inch-based threads, but you must first determine the pitch by looking at the number of treads per inch (TPI; for example, = 0.050 and ≈ 0.077), and your result will only land near a tap drill size (not directly on one).
  • Example (inch coarse): For -14, 1in ÷ 14 = 0.071in; 0.437in − 0.071in = 0.366in;
    • The drill sizes that are near this are 9.3 mm (0.366in) and letter U (0.368in). In addition, 9.5 mm (0.374in), and in (0.375in) will work well, although major minus pitch by itself does not tell you this; but the 85% ± 2 pp guideline supports it.
  • Example (inch fine): For -20, 1in ÷ 20 = 0.050in; 0.437in − 0.050in = 0.387in;
    • The drill sizes that are near this are letter W (0.386in) and in (0.391in). In addition, 10 mm (0.393in), and letter X (0.397in) will work well, although major minus pitch by itself does not tell you this; but the 90% ± 2 pp guideline supports it.
• For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the only possible one, but it is a good one for general use.
  • Example (metric coarse): For M7.0×1.0, major minus pitch yields 6.0, but 6.1 also works well.
  • Example (metric fine): For M7.0×0.5, major minus pitch yields 6.5, which at 92.9% happens to be an example that pushes over the outer bound of the 90% ± 2 pp, but major minus pitch is still valid, although smaller drills (6.3 mm,, 6.4 mm) will work well.

Chart

Drill bit diameter		Fractional size	Drill wire  gauge^[2] ^[3]	Tap size^[4] ^[5] ^[6]	Clearance		Thread depth^†^[7] ^[8] (%)	Outer diameter
(mm, 4 d.p.)	(in, 5 d.p.)	(in)			Close fit^[9]	Free fit^[10]
0.0483	0.00190		107
0.0500	0.00197
0.0584	0.00230		106
0.0686	0.00270		105
0.0787	0.00310		104
0.0889	0.00350		103
0.0991	0.00390		102
0.1000	0.00394
0.1092	0.00430		101
0.1194	0.00470		100
0.1295	0.00510		99
0.1397	0.00550		98
0.1499	0.00590		97
0.1600	0.00630		96
0.1702	0.00670		95
0.1803	0.00710		94
0.1905	0.00750		93
0.2007	0.00790		92
0.2000	0.00787
0.2108	0.00830		91
0.2210	0.00870		90
0.2311	0.00910		89
0.2413	0.00950		88
0.2500	0.00984
Drill bit diameter		Fractional size	Drill wire  gauge	Tap size	Clearance		Thread depth^†^[11] (%)	Outer diameter
(mm, 4 d.p.)	(in, 5 d.p.)	(in)			Close fit	Free fit
0.2540	0.01000		87
0.2667	0.01050		86
0.2794	0.01100		85
0.2921	0.01150		84
0.3000	0.01181
0.3048	0.01200		83
0.3175	0.01250		82
0.3302	0.01300		81
0.3429	0.01350		80
0.3500	0.01378
0.3680	0.01449		79
0.3969	0.01563			0000-160^‡	0.02400in			0.021 in
0.4000	0.01575
0.4064	0.01600		78
0.4200	0.01654
0.4400	0.01732
0.4500	0.01772
0.4572	0.01800		77
0.4600	0.01811
0.4800	0.01890
0.5000	0.01969
0.5080	0.02000		76
0.5334	0.02100		75
0.5500	0.02165
Drill bit diameter		Fractional size	Drill wire  gauge	Tap size	Clearance		Thread depth^†^[12] (%)	Outer diameter
(mm, 4 d.p.)	(in, 5 d.p.)	(in)			Close fit	Free fit
0.5715	0.02250		74
0.6000	0.02362
0.6096	0.02400		73
0.6350	0.02500		72
0.6500	0.02559
0.6604	0.02600		71	000-120^‡	0.03700in
0.7000	0.02756
0.7112	0.02800		70
0.7417	0.02920		69
0.7500	0.02953
0.7874	0.03100		68
0.7938	0.03125
0.8000	0.03150
0.8128	0.03200		67
0.8382	0.03300		66
0.8500	0.03346
0.8890	0.03500		65	00-90^‡	0.05200in
0.9000	0.03543
0.9144	0.03600		64
0.9398	0.03700		63
0.9500	0.03740
0.9652	0.03800		62
0.9906	0.03900		61
1.0000	0.03937
1.0160	0.04000		60
Drill bit diameter		Fractional size	Drill wire  gauge	Tap size	Clearance		Thread depth^†^[13] (%)	Outer diameter
(mm, 4 d.p.)	(in, 5 d.p.)	(in)			Close fit	Free fit
1.0414	0.04100		59
1.0500	0.04134
1.0668	0.04200		58
1.0922	0.04300		57
1.1000	0.04331
1.1500	0.04528
1.1811	0.04650		56
1.1906	0.04688			0-80	0.06350in	0.07000in
1.2000	0.04724
1.2500	0.04921
1.3000	0.05118
1.3208	0.05200		55
1.3500	0.05315
1.3970	0.05500		54
1.4000	0.05512
1.4500	0.05709
1.5000	0.05906
1.5113	0.05950		53	1-64, #1-72	0.07600in	0.08100in
1.5500	0.06102
1.5875	0.06250
1.6000	0.06299			M2×0.4	2.2mm
1.6129	0.06350		52
1.6500	0.06496
1.7000	0.06693
1.7018	0.06700		51	2-56	0.08900in	0.09600in
1.7500	0.06890			M2.2×0.45	2.25mm
Drill bit diameter		Fractional size	Drill wire  gauge	Tap size	Clearance		Thread depth^†^[14] (%)	Outer diameter
(mm, 4 d.p.)	(in, 5 d.p.)	(in)			Close fit	Free fit
1.7780	0.07000		50	2-56, #2-64	0.08900in	0.09600in
1.8000	0.07087
1.8500	0.07283
1.8542	0.07300		49
1.9000	0.07480
1.9304	0.07600		48
1.9500	0.07677
1.9600	0.07717			3-48	0.10400in	0.11000in	81
1.9700	0.07756			3-48	0.10400in	0.11000in	79
1.9844	0.07813			3-48	0.10400in	0.11000in	78
1.9939	0.07850		47	3-48	0.10400in	0.11000in	76
2.0000	0.07874			3-48	0.10400in	0.11000in	75
2.0100	0.07913			3-48	0.10400in	0.11000in	74
2.0200	0.07953			3-48	0.10400in	0.11000in	72
2.0300	0.07992			3-48	0.10400in	0.11000in	71
2.0400	0.08031			3-48 #3-56	0.10400in	0.11000in	69 81
2.0500	0.08071			3-48 #3-56 M2.5×0.45	0.10400in	0.11000in	68 79
2.0574	0.08100		46	3-48 #3-56	0.10400in	0.11000in	66 77
2.0700	0.08150			3-48 #3-56	0.10400in	0.11000in	65 75
2.0828	0.08200		45	3-48 #3-56	0.10400in	0.11000in	66 74
2.0900	0.08228			3-48 #3-56	0.10400in	0.11000in	62 72
2.1000	0.08268			3-48 #3-56	0.10400in	0.11000in	60 70
2.1100	0.08307			3-48 #3-56	0.10400in	0.11000in	59 69
2.1200	0.08346			3-56	0.10400in	0.11000in	67
2.1300	0.08386			3-56	0.10400in	0.11000in	65
2.1400	0.08425			3-56	0.10400in	0.11000in	63
2.1500	0.08465			3-56 M2.5×0.35	0.10400in	0.11000in	62
2.1600	0.08504			3-56	0.10400in	0.11000in	60
2.1700	0.08543			3-56	0.10400in	0.11000in	59
2.1844	0.08600		44	4-36	0.11600in	0.12850in	81
2.1900	0.08622			4-40	0.11600in	0.12850in	81
2.2000	0.08661			4-40	0.11600in	0.12850in	78
2.2100	0.08701			4-40	0.11600in	0.12850in	77
2.2200	0.08740			4-40	0.11600in	0.12850in	76
2.2300	0.08780			4-40	0.11600in	0.12850in	75
2.2400	0.08819			4-40	0.11600in	0.12850in	73
2.2500	0.08858			4-40	0.11600in	0.12850in	72
2.2600	0.08898			4-40	0.11600in	0.12850in	71
2.2606	0.08900		43	4-40	0.11600in	0.12850in	71
2.2700	0.08937			4-40	0.11600in	0.12850in	70
2.2800	0.08976			4-40	0.11600in	0.12850in	68
2.2900	0.09016			4-40 #4-48	0.11600in	0.12850in	67 81
2.3000	0.09055			4-40 #4-48	0.11600in	0.12850in	66 79
2.3100	0.09094			4-40 #4-48	0.11600in	0.12850in	65 78
2.3200	0.09134			4-40 #4-48	0.11600in	0.12850in	64 76
2.3300	0.09173			4-40 #4-48	0.11600in	0.12850in	63 75
2.3400	0.09213			4-40 #4-48	0.11600in	0.12850in	61 74
2.3500	0.09252			4-40 #4-48	0.11600in	0.12850in	60 72
2.3749	0.09350		42	4-48	0.11600in	0.12850in	69
2.3813	0.09375
2.4000	0.09449
2.4384	0.09600		41
2.4500	0.09646
2.4892	0.09800		40
2.5000	0.09843			M3×0.5	3.2mm		75
2.5273	0.09950		39	5-40	0.12850in	0.13600in	78
2.5781	0.10150		38	5-40	0.12850in	0.13600in	72
2.6000	0.10236
2.6416	0.10400		37	5-44	0.12850in	0.13600in	71
2.7000	0.10630
2.7051	0.10650		36	6-32	0.14400in	0.14950in	77	0.14in
2.7500	0.10827
2.7781	0.10938
2.7940	0.11000		35
2.8000	0.11024
2.8194	0.11100		34
2.8702	0.11300		33	6-40		0.1563in		0.14in
2.9000	0.11417			M3.5×0.6
2.9464	0.11600		32
3.0000	0.11811
3.0480	0.12000		31	6-48
3.1000	0.12205
3.1750	0.12500
3.2000	0.12598
3.2500	0.12795
3.2639	0.12850		30
3.3000	0.12992			M4×0.7	4.10mm		75
3.4000	0.13386
3.4544	0.13600		29	8-32, #8-36	0.16950in	0.17700in	69
3.5000	0.13780			M4×0.5	4.10mm		60
3.5687	0.14050		28	8-40
3.5719	0.14063
3.6000	0.14173
3.6576	0.14400		27
3.7000	0.14567
3.7338	0.14700		26
3.7500	0.14764
3.7973	0.14950		25	10-24	0.19600in	0.20100in	75
3.8000	0.14961
3.8608	0.15200		24
3.9000	0.15354
3.9116	0.15400		23
3.9688	0.15625
3.9878	0.15700		22
4.0000	0.15748
4.0386	0.15900		21	10-32	0.1960in	0.2010in
4.0894	0.16100		20
4.1000	0.16142
4.2000	0.16535			M5×0.8	5.10mm		75
4.2164	0.16600		19
4.2500	0.16732
4.3053	0.16950		18
4.3656	0.17188
4.3942	0.17300		17
4.4000	0.17323
4.4958	0.17700		16	12-24	0.22100in	0.22800in	72
4.5000	0.17717
4.5720	0.18000		15
4.6000	0.18110
4.6228	0.18200		14
4.6990	0.18500		13
4.7000	0.18504
4.7500	0.18701
4.7625	0.18750
4.8000	0.18898
4.8006	0.18900		12
4.8514	0.19100		11
4.9000	0.19291
4.9149	0.19350		10
4.9784	0.19600		9
5.0000	0.19685			M6×1.0	6.10mm		75
5.0546	0.19900		8
5.1000	0.20079
5.1054	0.20100		7	-20	0.25700in	0.26600in	72
5.1594	0.20313
5.1816	0.20400		6
5.2000	0.20472			M6×0.75 ^[15]	6.10mm		60
5.2197	0.20550		5
5.2500	0.20669
5.3000	0.20866
5.3086	0.20900		4
5.4000	0.21260
5.4102	0.21300		3	-28	0.25700in	0.26600in	80
5.5000	0.21654			-28	0.25700in	0.26600in	70
5.5563	0.21875			-28 -32 (-32 UNEF for glow plugs)	0.25700in	0.26600in	68
5.6000	0.22047			-28	0.25700in	0.26600in	63
5.6134	0.22100		2	-28	0.25700in	0.26600in	60
5.7000	0.22441
5.7500	0.22638
5.7912	0.22800		1
5.8000	0.22835
5.9000	0.23228
5.9436	0.23400		A
5.9531	0.23438
6.0000	0.23622
6.0452	0.23800		B
6.1000	0.24016			M7×1.0			75
6.1468	0.24200		C
6.2000	0.24409
6.2484	0.24600		D
6.2500	0.24606
6.3000	0.24803
6.3500	0.25000
			E
6.4000	0.25197
6.5000	0.25591			M7×0.5
6.5278	0.25700		F	-18	0.32300in	0.33200in	77
6.6000	0.25984
6.6294	0.26100		G
6.7000	0.26378
6.7469	0.26563			-18			74
6.7500	0.26575
6.7564	0.26600		H
6.8000	0.26772
6.9000	0.27165			M8×1.25			75
6.9088	0.27200		I	-24	0.32300in	0.33200in	75
7.0000	0.27559
7.0358	0.27700		J	-18			50
7.1000	0.27953			M8×1.0			75
7.1374	0.28100		K
7.1438	0.28125			-32
7.2000	0.28346
7.2500	0.28543
7.3000	0.28740
7.3660	0.29000		L
7.4000	0.29134
7.4930	0.29500		M
7.5000	0.29528
7.5406	0.29688
7.6000	0.29921
7.6708	0.30200		N
7.7000	0.30315
7.7500	0.30512
7.8000	0.30709
7.9000	0.31102
7.9375	0.31250			-16	0.38600in	0.39700in	77
8.0000	0.31496
8.0264	0.31600		O
8.1000	0.31890
8.2000	0.32283
8.2042	0.32300		P
8.2500	0.32480
8.3000	0.32677
8.3344	0.32813
8.4000	0.33071
8.4328	0.33200		Q	-24	0.38600in	0.39700in	79
8.5000	0.33465			M10×1.5
8.6000	0.33858
8.6106	0.33900		R
8.7000	0.34252
8.7313	0.34375
8.7500	0.34449			M10×1.25
8.8000	0.34646
8.8392	0.34800		S
8.9000	0.35039
9.0000	0.35433			M10×1.0 ^(spark plug)
9.0932	0.35800		T
9.1000	0.35827
9.1281	0.35938
9.2000	0.36220
9.2500	0.36417
9.3000	0.36614
9.3472	0.36800		U	-14	0.45310in	0.46870in	75
9.4000	0.37008
9.5000	0.37402
9.5250	0.37500
9.5758	0.37700		V
9.6000	0.37795
9.7000	0.38189
9.7500	0.38386
9.8000	0.38583
9.8044	0.38600		W
9.9000	0.38976
9.9219	0.39063			-20	0.45313in	0.46785in	72
10.0000	0.39370
10.0838	0.39700		X
10.2616	0.40400		Y
10.3188	0.40625			-40
10.4902	0.41300		Z
10.5000	0.41339			M12×1.75			75
10.7000	0.42126			M12×1.5			75
10.7156	0.42188			-13	0.51563in	0.53125in	78
10.900	0.42913			M12×1.25 ^(spark plug)
11.0000	0.43307
11.1125	0.43750
11.5000	0.45276
11.5094	0.45313			-20	0.51563in	0.53125in	72
11.9063	0.46875			-12	0.56250in		87
12.0000	0.47244
12.2000	0.48031			M14×2			75
12.3031	0.48438			-12	0.56250in		68
12.5000	0.49213
12.7000	0.50000			-18	0.56250in		87
				M14×1.5			75
12.8000	0.50393			M14×1.25 ^(spark plug)
13.0000	0.51181
13.0969	0.51563			-18	0.56250in		65
13.4938	0.53125			-11	0.62500in		79
13.5000	0.53150
13.8906	0.54688			-11	0.62500in		66
14.0000	0.55118
14.2000	0.55906			M16×2			75
14.2875	0.56250			-18	0.62500in		87
14.5000	0.57087
14.6844	0.57813			-18	0.62500in		65
14.7000	0.57874			M16×1.5			75
15.0000	0.59055
15.0813	0.59375
15.4781	0.60938
15.5000	0.61024
15.8750	0.62500
16.0000	0.62992
16.2719	0.64063			-10			84
16.5000	0.64961
16.6688	0.65625			-10			72
16.8000	0.66141			M18×1.5 ^(spark plug)
17.0000	0.66929
17.0656	0.67188
17.4625	0.68750			-16			77
17.5000	0.68898
17.8594	0.70313
18.0000	0.70866
18.2563	0.71875
18.5000	0.72835
18.6531	0.73438
19.0000	0.74803
19.0500	0.75000
19.4469	0.76563			-9			76
19.5000	0.76772
19.8438	0.78125			-9			65
20.0000	0.78740
20.2406	0.79688			-14			84
20.5000	0.80709
20.6375	0.81250			-14			67
21.0000	0.82677
21.0344	0.82813			-18 NS ^(spark plug)
21.4313	0.84375
21.5000	0.84646
21.8281	0.85938			1-8			87
22.0000	0.86614
22.2250	0.87500			1-8			77
22.5000	0.88583
22.6219	0.89063			1-8			67
23.0000	0.90551
23.0188	0.90625			1-12			87
23.4156	0.92188			1-12 1-14			72 84
23.5000	0.92520
23.8125	0.93750			1-14			67
24.0000	0.94488
24.2094	0.95313
24.5000	0.96457
24.6063	0.96875			-7			84
25.0000	0.98425
25.0031	0.98438			-7			76
25.4000	1.00000	1		-7			67
25.5000	1.00394
25.7969	1.01563
26.0000	1.02362
26.1938	1.03125			-12			87
26.5000	1.04331
26.5906	1.04688			-12			72
26.9875	1.06250
27.0000	1.06299
27.5000	1.08268
28.0000	1.10236
28.1781	1.10938			-7			76
28.5000	1.12205
28.5750	1.12500			-7			67
29.0000	1.14173
29.3688	1.15625			-12			87
29.5000	1.16142
29.7656	1.17188			-12			72
30.0000	1.18110
30.1625	1.18750			-6			87
30.5000	1.20079
30.5594	1.20313			-6			79
30.9563	1.21875			-6			72
31.0000	1.22047
31.3531	1.23438			-6			65
31.5000	1.24016
32.0000	1.25984
32.5000	1.27953
32.5438	1.28125			-12			87
32.9406	1.29688			-12			72
33.0000	1.29921
33.3375	1.31250			-6			87
33.5000	1.31890
33.7344	1.32813			-6			79
34.0000	1.33858
34.1313	1.34375			-6			72
34.5000	1.35827
34.5281	1.35938			-6			65
35.0000	1.37795
35.5000	1.39764
35.7188	1.40625			-12			87
36.0000	1.41732
36.1156	1.42188			-12			72
36.5000	1.43701

^†If theoretical thread percentage not given, assume 75% ± 10%
  Theoretical percentage of thread should not be relied upon for threads of included angles other than 60 degrees.
^‡See http://www.newmantools.com/taps/micro.htm for more information.

See also

• AN thread
• British standard pipe thread
• British Association screw threads
• British Standard Whitworth
• Drill bit sizes, a similar page including center drill sizes
• ISO metric screw thread
• National pipe thread
• Taps and dies
• United States Standard thread
• Unified Thread Standard

External links

• Tap Drill Sizes
• Metric Tap Drill Sizes
• Tap and drill chart
• BTA Drill Tube Reference Chart

Notes and References

1. Web site: Drill Bit Size Charts and Rule of Thumb.
2. Web site: Continuous Drill Bit Sizes . 2006-08-29 . https://web.archive.org/web/20060719084558/http://www.madison.k12.wi.us/toki/codrills.htm . 2006-07-19 . dead .
3. Web site: Decimal Equivalents . Ohio State University . 2006-08-29 . https://web.archive.org/web/20060902095350/http://www.physics.ohio-state.edu/~kelch/decimal.html . 2006-09-02 . dead .
4. Web site: Tap Drill Sizes and Calculator. newmantools.com. 2006-08-04.
5. Web site: Tap Drill Sizes for Universal and M-Profile Screw Threads. precisiontwistdrill.com. 2006-08-04.
6. Web site: NC, NF, NEF to one inch in diameter. Sizes.com. 2006-09-01. dead. https://web.archive.org/web/20060929162504/http://www.sizes.com/tools/thread_NCNF.htm. 2006-09-29.
7. Web site: High performance taps . guhring.com. 2010-10-07.
8. Web site: Tap Drill Sizes. widell.com. 2006-09-01. dead. https://web.archive.org/web/20061114071651/http://www.widell.com/drillsiz.html. 2006-11-14.
9. Web site: Tap & Clearance Drills For Common Screws. Small Parts Inc.. 2010-10-07 .
10. Web site: Tap Drill Sizes. efunda.com. 2006-08-04.
11. Web site: High performance taps . guhring.com. 2010-10-07.
12. Web site: High performance taps . guhring.com. 2010-10-07.
13. Web site: High performance taps . guhring.com. 2010-10-07.
14. Web site: High performance taps . guhring.com. 2010-10-07.
15. http://www.littlemachineshop.com/reference/tapdrillsizes.pdf