Studs

Standard nut

Thin (lock) nut

Plain washer

Example 1

An M5 hexagon head bolt will lie within product grade A tolerances and will have a shank diameter lying between 5.00 and 4.82 mm inclusive.

Example 2

An M36 hexagon head bolt will lie within product grade B tolerances and will have a shank diameter lying between 36.00 and 35.38 mm inclusive.

Example 3

An M16 hexagon head bolt will have a shank diameterlying between 16 and 15.73 mm inclusive if it is toproduct grade A tolerances. If it is to product grade B tolerances, it will have a shank diameter lying between 16 and 15.57 mm inclusive.

Note: The above system of tolerancing applies to all the other dimensions for the fasteners in these tables:

• Examine the table in Section 4.1.14. All the dimensions in this table refer to screwed fasteners with product grade C tolerances. Comparing this table with the previous examples shows that the fasteners made to the product grade C specifications have much coarser tolerances than those manufactured to product grades A and B tolerances.

• An M12 bolt to product grade A has a shank diameter(cQ lying between 12 and11. 73 mm (a tolerance of 0.27 mm), whereas an M12 bolt made product grade C will have a shank diameter (ds) lying between 12.77 and 11.3 mm (a tolerance of 1.4 mm). Product grade B does not apply to this size of bolt.

Note: The old terminology of 'black' (hot forged) and 'bright/precision' (cold headed or machined from hexagon bar) bolts and nuts no longer applies. However hot forged (black) bolts and nuts made to special order would only have been made to product grade C.

All the previous notes refer to hexagon head bolts,screws and nuts with coarse pitch threads. Bolts have a plain shank between the thread and the head, whereas a screw is threaded virtually all the way up to the head. The following tables and standards (Sections 4.1.22 to 4.1.26) refer to a corresponding fine pitch series of screwed fasteners. These fine pitch series of screwed fasteners are only available in product grades A and B.

4.1.22 BS EN ISO 8765: 2001 Hexagon head bolts with metricfine pitch threads - product grades A and B

4.1.23 BS EN ISO 8676: 2001 Hexagon head screws with metric fine pitch threads - product grades A and B

4.1.24 BS EN ISO 8673: 2001 Hexagon nuts style 1 with metric fine pitch threads - product grades A and B

4.1.25 BS EN ISO 8674: 2001 Hexagon nuts style 2 with metric fine pitch threads -product grades A and B

4.1.26 BS EN ISO 8675: 2001 Hexagon thin nuts with metric fine pitch threads - product grades A and B

Note: Symbols and descriptions of dimensions are specified in ISO 225.

(1) Incomplete thread u ≤ 2 P

Example for the designation of a hexagon head bolt with thread M12, nominal length I = 80 mm and property class 8.8:

Hexagon head bolt ISO 4014 - M12 ×80 - 8.8

BS EN ISO 4014: 2001 Table 1

Preferred threads

BS EN ISO 4014: 2001 Table 2

Preferred threads

Note: Symbols and descriptions of dimensions are specified in ISO 225.

Note: Symbols and descriptions of dimensions are specified in ISO 225.

(1) Incomplete thread u ≤ 2 P.

(2) d_s = pitch diameter.

Example for the designation of a hexagon head screwwith thread size M12, nominal length I= 80 mm and property class 8.8:

Hexagon head screw ISO 4017- M12 x80 –8.8

BS EN ISO 4017: 2001 Table 1

Preferred threads

BS EN ISO 4017: 2001 Table 2

Non-preferred threads

Note: Symbols and descriptions of dimensions are specified in ISO 225.

Example for the designation of a hexagon head screw with thread size M12, nominal length I= 80 mm and property class 4.6:

Hexagon head screw ISO 4018- M12x 80 –4.6

BS EN ISO 4018: 2001 Table 1

Preferred threads

BS EN ISO 4018: 2001 Table 2

Non-preferred threads Dimensions in mm

Example for the designation of a hexagon nut, style1, with thread size d = M12 and property class 8:

Hexagon nut ISO 4032 - M12 - 8

Example for the designation of a hexagonnut with thread size d = M12 and property class 5:

Hexagon nut ISO 4034 – M12 – 5

Dimensions in mm

Dimensions in mm

Dimensions in mm

Dimensions in mm

Example for the designation of a hexagon thin nut with metric thread d = M6 made from steel with HV 110 min. (st):

Hexagon nut ISO 4036 - M6-st

Note: Symbols and descriptions of dimensions are specified in ISO 225.

(1) Incomplete thread u ≤ 2 P

BS EN ISO 8765: 2001 Table 1

Preferred threads

BS EN ISO 8765: 2001 Table 2

Non-preferred threads

Note: Symbols and descriptions of dimensions are specified in ISO 225.

(1) Incomplete thread u ≤ 2 P.

(2) d_s = pitch diameter.

BS EN ISO 8676: 2001 Table 1

Preferred threads

BS EN ISO 8676: 2001 Table 2

Non-preferred threads

Note: Symbols and descriptions of dimensions are specified in ISO 225.

Note: Symbols and descriptions of dimensions are specified in ISO 225.

Note: Symbols and descriptions of dimensions are specified in ISO 225.

When tested by the methods described in clause 8, the bolts, screws and studs shall, at room temperature, have the mechanical properties set out in BS EN ISO 898-1: 1999 Table 3.

BS EN ISO 898–1: 1999 Table 3

Mechanical properties of bolts, screws and studs

Sub clause No.	Mechanical property		Property class
			3.6	4.6	4.8	5.6	5.8	6.8	8.8a		9.8c	10.9	12.9
									d ≤ 16 mm	d > 16 mmb
5.1 and 5.2	Tensile strength, Rmd,e, N/mm2	nom.	300	400		500		600	800	800	900	1 000	1 200
		min.	330	400	420	500	520	600	800	830	900	1 040	1 220
5.3	Vickers hardness, HV,F > 98 N	min.	95	120	130	155	160	190	250	255	290	320	385
		max.	250						320	335	360	380	435
5.4	Brinell hardness, HB, F = 30D2	min.	90	114	124	147	152	181	238	242	276	304	366
		max.	238						304	318	342	361	414
		HRB	52	67	71	79	82	89	−	−	−	−	−
5.5	Rockwell hardness, HR	HRC	−	−	−	−	−	−	22	23	28	32	39
		HRB	99.5						−	−	−	−	−
		HRC	−						32	34	37	39	44
5.6	Surface hardness, HV 0.3	max.	−						− f
5.7	Lower yield stress, ReLg, N/mm2	nom.	180	240	320	300	400	480	−	−	−	−	−
		min.	190	240	340	300	420	480	−	−	−	−	−
5.8	Proof stress, Rp0.2, N/mm2	nom.	−						640	640	720	900	1080
		min.	−						640	660	720	940	1100
5.9	Stress under proofing load, 5p	Sp/ReL or Sp/Rp0 2	0.94	0.94	0.91	0.93	0.90	0.92	0.91	0.91	0.90	0.88	0.88
		N/mm2	180	225	310	280	380	440	580	600	650	830	970
5.10	Elongation after fracture, A	min.	25	22	14	20	10	8	12	12	10	9	8
5.11	Strength under wedge loadinge		The values for full size bolts and screws (not studs) shall not be smaller than the minimum values for tensile strength shown in 5.2
5.12	Impact strength, J	min.		−		25			30	30	25	20	15
5.13	Head soundness		no fracture
5.14	Minimum height of non − decarburized thread zone, E		−						$\frac{1}{2}$ H1			$\frac{2}{3}$ H1	$\frac{3}{4}$ H1
	Maximum depth of complete decarburization, G	mm	−						0.015

be tensile tested (e.g. due to head configuration).

^a For bolts of property class 8.8 in diameters d 16 mm, there is an increased risk of nut stripping in the case of inadvertent over − tightening inducting a load in excess of proofing load. Reference to ISO 898.2 is recommended.

^b For structural bolting the limit is 12 mm.

^c Applies only to nominal thread diameters d 16 mm.

^d Minimum tensile properties apply to products of nominal length I 2.5d. Minimum hardness applies to products of length I < 2.5d and other products which cannot

^e For testing of full − size bolts, screws and studs, the loads given in BS EN ISO 898–1: 1999 Tables 6 to 9 (of the full standard) shall be applied.

^f Surface hardness shall not be more than 30 Vickers points above the measured core hardness on the product when readings of both surface and core are carried out at HV 0.3. For property class 10.9, any increase in hardness at the surface which indicates that the surface hardness exceeds 390 HV is not acceptable.

^g In cases where the lower yield stress R_eL cannot be determined, it is permissible to measure the proof stress R_p0.2.

Mechanical properties to be determined

Two test programmes, A and B, for mechanical properties of bolts, screws and studs, using the methods described in clause 8, are set out in BSEN ISO 898-1: 1999 Table 5.

The application of programme B is always desirable, but is mandatory for products with breaking loads less than 500 kN. Programme A is suitable for machined test pieces and for bolts with a shank area less than the stress area.

BS EN ISO 898-1: 1999 Table 4

Key to test programmes (see BS EN ISO 898-1: 1999 Table 5)

Size	Bolts and screws with thread diameter d 4 mm or length 1 < 2.5d a	Bolts and screws with thread diameter d > 4 mm and length 1 > 2.5d
Test decisive for acceptance

^a Also bolts and screws withspecial head or shank configurations which are weaker than the threaded

BS EN ISO 898-1: 1999 Table 5

Test programmes A and B for acceptance purposes

a If the wedge loading test is satisfactory, the axial tensile test is not required.

b Minimum hardness applies only to products of nominal length l 2.5d and other products which cannot be tensile tested (e.g. due to head configuration).

c Hardness may be Vickers, Brinell or Rockwell. In case of doubt, the Vickers hardness test is decisive for acceptance.

d Special head bolts and screws with configurations which are weaker than the threaded section are excluded from wedge tensile testing requirements.

e Only for bolts, screws and studs with thread diameters d 16 mm and only if required by the purchaser.

f Only for property class 5.6.

g Only for bolts and screws with thread diameters d 16 mm and lengths too short to permit wedge load testing.

Note: These procedures apply to mechanical but not chemical properties.

Minimum ultimate tensile loads and proofing loads

See BS EN ISO 898-1: 1999 Tables 6 to 9.

BS EN ISO 898-1: 1999 Table 6

Minimum ultimate tensile loads ° ISO metric coarse pitch thread

^aWhere no thread pitch is indicated in a thread designation, coarse pitch is specified. This is given in ISO 261 and ISO 262.

^bFor structural bolting 50700, 68800 and 94500 N, respectively.

Marking symbols are shown in BS EN ISO 898-1: 1999 Table 1.

Marking of left-hand thread

Bolts and screws with left-hand thread shall be marked with the symbol shown in Fig 4, either on the top of the head or the point.

Marking is required for bolts and screws with nominal thread diameters 5 mm.

Alternative marking for left-hand thread may be used for hexagon bolts and screws asshown in Fig. 5.

Alternative marking

Alternative or optional permitted marking as stated in the sections Symbols, Identification and Marking of left-hand thread should be left to the choice of the manufacturer.

Trade (identification) marking

The trade (identification) marking of the manufacturer is mandatory on all products which are marked with property classes.

Proof load values

Proof load values are given in BS EN 20898-2: 1994 Table 2.

BS EN 20898-2: 1994 Table 2

Proof load values – Coarse thread

The nominal stress area A_sis calculated as follows:

$A_S=\text{?}\text{?}\frac{\pi }{4}{\left(\frac{d_2+d_3}{2}\right)}^2$

where:

d₂ = basic pitch diameter of the external thread (see ISO 724);

d₃ = minor diameter of the external thread;

d₃ 

$=\text{?}{d}_1\text{?}-\text{?}\frac{H}{6}$

where:

d₁ = basic pitch diameter of the external thread;

H = height of the fundamental triangle of the thread.

BS EN 20898-2: 1994 Table 3

Marking symbols for nuts with property classesin accordance with BS EN 20898-2 clause 3.1

Property class		4	5	6	8	9	10	12a or code symbol (clock-face system)
Alternative marking	either designation symbol.	4	5	6	8	9	10	12
	or code symbol (clock-face system)

^a The marking dot cannot be replaced by the manufacturer–s mark.

BS EN 20898-2: 1994 Table 4

Marking symbols for nuts with property classes in accordance with BS EN 20898-2 clause 3.2

Property class	04	05
Marking

Marking of left-hand thread

Nuts with left-hand thread shall be marked as shown in Fig. 1 on one bearing surface of the nut by indenting.

Marking is required for nuts with threads ≥ M5.

The alternative marking for left-hand thread shown in Fig. 2 may also be used.

Alternative marking

Alternative or optional permitted marking as stated in the sections Symbols, Identification and Marking of left-hand thread under Section 4.1.29 is left to the choice of the manufacturer.

Trade(identification) marking

The trade (identification) marking of the manufacturer is mandatory on all products covered by the obligatory marking requirementsfor property classes, provided this is possible for technical reasons. Packages, however, shall be marked in all cases.

Nuts with nominal heights ≥0.5d and < 0.8d (effective heights of thread ≥0.4d and < 0.6d)

Nuts with nominal heights ≥0.5d and < 0.8d (effective height of thread ≥0.4d and < 0.6d) are designated by a combination of two numbers: the secondindicates the nominal stress under proof load on ahardened test mandrel, while the first indicates that the load ability of a bolt-nut assembly is reduced in comparison with the loadability on a hardened test mandrel and also in comparison with a bolt-nut assembly described in Section 3.1. The effective loading capacity is not only determined by the hardness of the nut and the effective height of thread but also by the tensile strength of the botwith which the nut is assembled.BS EN ISO 898-6: 1996 Table 2 gives the designation system and the stresses under proof load of the nuts. Proof loads are shown in BS EN ISO 898-6: 1996 Table 3. A guide for minimum expected stripping strengths of the joints when these nuts are assembled with bolts ofvarious property classes is shown in BS EN ISO 898-6: 1996 Table 4.

Materials

Nuts of property classes 05, 8(style 1), 10 and 12 shall be hardened and tempered.

Nuts shall be made of steel conforming to the chemical composition limits specified in BS EN ISO 898-6: 1996 Table 5. The chemicalcomposition shall be analysed in accordance with relevant International Standards.

Mechanical properties

When tested by the methods described in clause 8, the nuts shall have the mechanical properties set out in BS EN ISO 898-6: 1996 Table 1under Section 4.1.30.

Proof load values

Proof load values are given in BS EN ISO 898-6: 1996 Table 3.

The nominal stress area As is calculated as follows:

$A_{\text{2}}\text{?}\text{=}\text{?}\frac{\text{π}}{\text{4}}{\left(\frac{d_2\text{+}{d}_3}{\text{2}}\right)}^{\text{2}}$

where:

d₂ = basic pitch diameter of the external thread (see ISO 724);

d₃ 

$d_3=\text{?}{d}_1-\frac{H}{6}$

d₁ = basic minor diameter of the external thread;

H = height of the fundamental triangle of the thread.

Dimensions

Note: Symbols and designations of dimensions are defined in ISO 225.

For broached sockets which are at the maximum limit of size the overcut resulting from drilling shall not exceed 1/3 of the length of any flat of the socket which is e/2.

See Figs 1 and 2, and BS EN ISO 10642: 2004 Table 1.

BS EN ISO 10642: 2004 Table 1

Dimensions

Note: Symbols and designations of dimensions are defined in ISO 225.

For broached sockets which are at the maximum limit of size the overcut resulting from drilling shall not exceed 1/3 of the length of any flat of the socket which is e/2.

Gauging of head

The top surface of the screw shall be located between the gauge surfaces A and B.

Requirements and reference International Standards

See BS EN ISO 10642: 2004 Tables 2 and 3.