Technical Information

Dimensional Specifications

DIN 931 & DIN 933

The drawing below shows unthreaded fasteners. The thread length of Metric bolts manufactured to DIN 931 and 933, with diameter d and thread length t, is:

t = 2d + 6mm up to 125mm;

t = 2d + 12mm from 125mm until 200mm; 2d + 25mm at 200mm and over.

(Click on the image to enlarge)

BS 1083

The drawing below shows unthreaded fasteners. The thread length of BSW or BSF bolts manufactured to BS1083, with diameter d and thread length t, is t = 2d.

(Click on the image to enlarge)

BS 1768

The drawing below shows unthreaded fasteners. The thread length of UNC or UNF bolts manufactured to BS1768, with diameter d and thread length t, is:

t = 2d + 1/4" up to a length of 6", where the formula becomes t = 2d + 1/2".

(Click on the image to enlarge)

How to measure

Measuring bolt diameter

Bolts can be accurately measured using a vernier.

For metric bolts, the prefix 'M' is added to denote Metric. For example, a 4mm diameter bolt is commonly known as an 'M4' bolt. Imperial bolts are measured in inches.

Measuring bolt length

The length of a Hexagon bolt is determined by measuring from underneath the head to the end of the bolt. If the bolt has a countersunk head, the full length of the bolt including head is measured.

Measuring threads

Metric bolts are identified by measuring the distance between the threads - a 1mm pitch bolt has 1mm between the threads.

The thread pitch of an imperial bolt is denoted by the amount of threads per inch.

See the thread charts on this page for more information.

A thread gauge can be used to identify bolts and nuts, although they are not in common usage. The Thread Detective is a quick and easy solution to the problem of identifying bolt and nut threadforms, allowing quick and precise identification of Metric, UNC & UNF bolts and nuts.

Thread Detective - Thread Identifier

Thread Charts

Metric

Metric bolts are identified by measuring the distance between the threads in millimetres - a 1mm pitch bolt has 1mm between the threads.

Diameter	Coarse	Fine	Extra Fine	Super Fine
M1	0.25	0.2
M1.6	0.35	0.2
M2	0.4	0.25
M2.5	0.45	0.35
M3	0.5	0.35
M4	0.7	0.5
M5	0.8	0.5
M6	1.0	0.75
M7	1.0	0.75
M8	1.25	1.0	0.75
M10	1.5	1.25	1.0	0.75
M12	1.75	1.5	1.25	1.0
M14	2.0	1.5	1.25	1.0
M16	2.0	1.5	1.0
M18	2.5	2.0	1.5	1.0
M20	2.5	2.0	1.5	1.0
M22	2.5	2.0	1.5	1.0
M24	3.0	2.0	1.5	1.0

Imperial

The thread pitch of an imperial bolt is denoted by the amount of threads per inch.

Diameter	UNC	UNF	BSW	BSF
No.4	40	48
No.6	32	40
No.10 / 3/16	24	32	24	32
1/4	20	28	20	26
5/16	18	24	18	22
3/8	16	22	16	20
7/16	14	20	14	18
1/2	13	20	12	16
9/16	12	18	12	16
5/8	11	18	11	14
3/4	10	16	10	12

BA

BA is an imperial threadform. The thread pitch of an imperial bolt is denoted by the amount of threads per inch.

BA number	TPI	Dia (inch)
6	47.9	0.11
4	38.5	0.142
3	34.8	0.161
2	31.4	0.185
0	25.4	0.236

Mechanical Properties

Metric

Property	4.6	8.8 <= M16	8.8 > M16	10.9	12.9
Min Tensile N/mm2	400	800	830	1040	1220
Min Lower Yield Stress N/mm2	240
Min Proof Stress N/mm2		640	660	940	1100
Hardness Min HRC		22	23	32	39
Hardness Max HRC		32	34	39	44

BSW & BSF

Property	R	T	V
Min Tensile tonf/in2	45	55	65
Min Yield Stress tonf/in2	34	41	52
Hardness Brinell	201/285	248/335	293/370

UNC & UNF

Property	S	T	V
Min Tensile tonf/in2	50	55	65
Proof Stress tonf/in2	38	41	49.5
Hardness Brinell	223/310	248/335	293/370

Torque figures

Metric coarse

	M6	M8	M10	M12	M14	M16	M20	M22	M24	M30	M36	M42
4.6 kgf m	0.46	1.12	2.23	3.89	6.21	9.65	18.8	25.6	32.6	64.7	113	181
8.8 kgf m	1.23	3.0	5.95	10.35	16.5	25.7	50.2	68.3	86.6	172	300	478
10.9 kgf m	1.73	4.22	8.35	14.6	23.2	36.2	70.7	96	122	242	423	678

Metric fine

	M6	M8	M10	M12	M14	M16	M20	M22	M24	M30	M36
4.6 kgf m	0.50	1.20	2.35	4.24	6.72	10.3	20.9	28.1	35.4	71.5	120
8.8 kgf m	1.34	3.2	6.25	11.3	17.9	27.3	55.7	75.0	94.5	189	316
10.9 kgf m	1.90	4.52	8.8	15.9	25.2	38.5	78.5	105	132	268	448

UNC

	1/4	5/16	3/8	7/16	1/2	9/16	5/8	3/4	7/8	1	1.1/8	1.1/4	1.3/8	1.1/2
S lbf ft	9	20	35	56	85	123	170	300	485	730	1035	1460	1920	2540
T lbf ft	10	21	36	58	88	127	175	311	500	750	1065	1500	1965	2610
V lbf ft	12	25	45	73	111	160	212	393	632	950	1345	1900	2480	3300

 

UNF

	1/4	5/16	3/8	7/16	1/2	9/16	5/8	3/4	7/8	1	1.1/8	1.1/4	1.3/8	1.1/2
S lbf ft	11	22	40	62	96	137	192	335	535	795	1075	1500	2040	2690
T lbf ft	12	23	41	64	99	141	195	345	650	820	1100	1540	2100	2760
V lbf ft	14	28	50	81	125	180	238	435	695	1000	1390	1950	2650	3500

BSW

	1/4	5/16	3/8	7/16	1/2	9/16	5/8	3/4	7/8	1	1.1/8	1.1/4	1.3/8	1.1/2
R lbf ft	8	17	30	47	70	105	145	255	410	620	875	1235	-	2150
V lbf ft	12	25	45	72	107	160	210	390	628	945	1330	1890	-	3280

BSF

	1/4	5/16	3/8	7/16	1/2	9/16	5/8	3/4	7/8	1	1.1/8	1.1/4	1.3/8	1.1/2
R lbf ft	9	18	32	51	77	112	155	268	432	650	930	1300	1730	2270
V lbf ft	14	27	49	78	118	173	224	410	660	995	1420	1990	2630	3480