What is Proof Load?

The Proof Load is defined as the greatest load than can be applied to a fastener that will not strain it beyond its elastic limit. In other words, the fastener must not deform and it must remain with it's elastic region when it is loaded up to its maximum proof load. Typically the proof load is between 85 to 95% of the yield strength.

According to ISO 225 and ISO 965-1 the following definition applies:

F_p = Proof Load, measured in N (Newtons)

What is Yield Strength?

The Yield Strength is defined as the amount of stress at which a predetermined amount of permanent deformation occurs.

What is Tensile Strength?

Tensile Strength is a measurement of the amount of force required to pull something until it fractures. In other words, the tensile strength of a fastener is the maximum amount of tensile strength it can handle before failure.

R_m = Tensile Strength, measured in N/mm² or MPa

Which nuts can come in higher tensile grades?

Fastener grade ranges are always given within the specification standard for particular nuts. We must ensure that a non-specified fastener is not quoted as a higher tensile one.

For example, it is common practice for customers to ask for Whitworth Grade 8 nuts. However, BSW/Whitworth nuts come in letter grades only. Or for customers to ask for lock nuts (thin) to be made in grade 8 - whereas these fasteners can not be torqued to grade 8 figures because there is not enough thread engagement.

See the following table for those standards covered under ISO 898-2 standard.

This specification only covers metric fasteners.

If a customer requests a fastener to a grade that is not specified within it's dimensional specification, it will be made to within the hardness limits below.

ISO 898-2:2012

Hardness limits of nuts according to ISO 898-2:2012 Property class 04 to 12.

CLASS	04		05		5		6		8		9		10		12
Thread	min	max	min	max	min	max	min	max	min	max	min	max	min	max	min	max
	Brinell Hardness - HB
<M16	179	287	259	336	124	287	143	287	190	287	179	287	259	336	280	336
<M39	179	287	259	336	139	287	162	287	221	336	179	287	259	336	259	336
M8x1<M16x1.5	179	287	259	336	166	287	179	287	238	336	-	-	280	336	280	336
M16x1.5<M39x3.0	179	287	259	336	181	287	221	287	280	336	-	-	247	336	-	-

DIN267 part 3: 1967 Mechanical Properties of Nuts

GRADE/CLASS	TENSILE STRENGTH	YIELD STRENGTH	DIN267:1960 CLASS
	N/square mm, min	N/square mm, min
3.6	340	200	4A
4.6	400	240	4D
4.8	400	320	4S
5.6	500	300	5D
5.8	500	400	5S
6.6	600	360	6D
6.8	600	480	6S
6.9	600	540	6G
8.8	800	640	8G
10.9	1000	900	10K
12.9	1200	1080	12K
14.9	1400	1260	-

BS1083 - Mechanical Properties of Finished Steel Hexagon Nuts

For nuts manufactured from bar, the Brinell hardness numbers are given for guidance only and are not part of the requirements for this standard. When nuts are manufactured by cold forming from round wire, with or without subsequent heat treatment, the Brinell hardness numbers apply as part of the requirements of this standard.

GRADE	APPLICATION	Ultimate Tensile Stress	Hardness - Brinell
		ton/square inch
A	Nuts for A, B, P & R bolts	28 min	120-235
P	Nuts for T bolts	35 min	152-240
R	Nuts for V bolts	45 min	201-271
T	Nuts for X bolts	55 min	248-335

Comparison of strength Grades between BS1768 and BS970

Indicative only

GRADE	BS1768 Tensile	BS1768 Tensile	BS970:1983 Tensile
	min	min
	ton f/m2	N/mm2	Brinell Hardness
P	35	541	550-700
S	50	772	775-925
T	55	849	850-1000
V	65	1004	1000-1150
X	75	1158	1150-1300

British Fastener Grades

GRADE	ton/in2	Brinell Hardness	Vickers Hardness	Rockwell C	N/mm2 & MPa
P	35-45	163-207	168-212		554-678
Q	40-50	187-229	192-234		616-770
R	45-55	207-248	212-253	-22	678-847
S	50-60	229-277	234-282	-27	770-939
T	55-65	248-302	253-310	22-31	847-1016
U	60-70	277-321	282-332	27-33	939-1093
V	65-75	302-341	310-356	31-36	1016-1155
W	70-80	321-363	332-382	33-39	1093-1232
X	75-85	341-388	356-409	36-41	1155-1309
Y	80-90	363-401	382-424	39-42	1232-1355

BS3692 - Mechanical Properties of Finished Steel Hexagon Nuts

Mechanical properties apply to metric ISO thread with nominal thread diameters up to and including 39mm and with heights of not less than 0.8D made of carbon steel or low alloy steel and when tested at room temperature.

GRADE	Proof Load Stress	Hardness - Brinell	Hardness - Rockwell C	Hardness - Vickers
	N/square mm	max	max	max
4	400	302	30	310
5	500	302	30	310
6	600	302	30	310
8	800	302	30	310
10	1000	353	36	370
12	1200	375	39	395

EN ISO 898-1:2013

Mechanical properties of nuts according to EN ISO 898-1:2013 Property class 4.6 to 12.9.

No.	Mechanical properties		property classes
No.	Mechanical properties		4.6	4.8	5.6	5.8	6.8	8.8 d<16 mmᵃ	8.8 d>16 mmᵇ	9.8 d<16 mm	10.9	12.9
1	Tensile strength, Rm, MPa	nom. °	400		500		600	800		900	1000	1200
1	Tensile strength, Rm, MPa	min.	400	420	500	520	600	800	830	900	1040	1220
2	Lower proof stress ReL ᵈ, MPa	nom. ᶜ	240	-	300	-	-	-	-	-	-	-
2	Lower proof stress ReL ᵈ, MPa	min.	240	-	300	-	-	-	-	-	-	-
3	Yield strength, Rp0.2, MPa	nom. ᶜ	-	-	-	-	-	640	640	720	900	1080
3	Yield strength, Rp0.2, MPa	min.	-	-	-	-	-	640	660	720	940	1100
4	Yield strength at 0.0048 d for whole screw, Rpf, MPa	nom. ᶜ	-	320	-	400	480	-	-	-	-	-
4	Yield strength at 0.0048 d for whole screw, Rpf, MPa	min.	-	340ᵉ	-	420ᵉ	480ᵉ	-	-	-	-	-
5	Proof stress, Spᶠ, MPa	nom.	225	310	280	380	440	580	600	650	830	970
5	Stress during proofing load testing ᴼ		0,94	0,91	0,93	0,90	0,92	0,91	0,91	0,90	0,88	0,88
6	Elongation after fracture (test specimen), A, %	min.	22	-	20	-	-	12	12	10	9	8
7	Contraction after fracture (test specimen), Z, %	min.	-					52		48	48	44
8	Elongation after fracture, Af (whole screw)	min.	-	0,24	-	0,22	0,20	-	-	-	-	-
9	Ductility in event of head soundness test		Inget brott
10	Vickers hardness, HV F ≥ 98 N	min.	120	130	155	160	190	250	255	290	320	385
10	Vickers hardness, HV F ≥ 98 N	max.	220ᵍ				250	320	335	360	380	435
11	Brinell hardness, HBW F = 30 D²	min.	114	124	147	152	181	238	242	276	304	366
11	Brinell hardness, HBW F = 30 D²	max.	209ᵍ				238	304	318	342	361	414
12	Rockwell hardness, HRB	min.	67	71	79	82	89	-
	Rockwell hardness, HRB	max.	95,0ᵍ				99,5	-
	Rockwell hardness, HRC	min.	-					22	23	28	32	39
	Rockwell hardness, HRC	max.	-					32	34	37	39	44
13	Surface hardness, HV 0.3	max.	-					h			h, i	h, j
14	Min. height of non-decarburised zone, E, mm	min.	-					½ H1			⅔ H1	¾ H1
14	Max. depth of complete decarburisation, G, mm	max.	-					0,015
15	Reduction in hardness after re-annealing, HV	max.	-					20
16	Fracture torque, MB,Nm	min.	-					regarding to ISO 898-7
17	Impact strength, Kᵥᵏ˴ˡ, J	min.	-		27	-		27	27	27	27	m
18	Surface defects		ISO 6157-1ⁿ									ISO 6157-3

a) The values do not apply to structural bolts.
b) For structural bolts ≥ M12.

c) Nominal values are only specified in order to indicate property class in the designation system.
d) If the lower proof stress ReL cannot be determined, it is permitted to measure the yield strength Rp0.2.
e) For property classes 4.8, 5.8 and 6.8, the values for Rpf min are under investigation.
f) Proof loads are specified in SS-EN ISO 898-1:2013.
g) Hardness determined at the end of the screw must be max. 250 HV, 238 HB or 99.5 HRB.
h) The surface hardness may not be more than 30 Vickers units higher than the measured core hardness determined with HV 0.3.
i) No surface hardness exceeding 390 HV is permitted.
j) No surface hardness exceeding 435 HV is permitted.
k) The values are determined at -20˚C.
l) Applies to d ≥ 16 mm.
m) Value Kᵥ is under investigation.
n) ISO 6157-3 can be used by agreement between manufacturer and purchaser.
o) Sp,nom / ReL min or Sp,nom / Rp0.2 min or Sp,nom / Rpf min

EN ISO 898-5:2012 Mechanical Properties of fasteners made of steel

This standard only concerns mechanical properties of fasteners which are not under tensile stress. It does not apply to fasteners that require special properties such as

specified tensile stresses
weldability
corrosion resistance
Ability to work in temperatures under 50 and above 250 degrees Celsius

		14H	17H	22H	33H	45H
VICKERS	min	140	170	220	330	450
	max	290	345	300	440	560
HARDNESS - BRINELL	min	133	162	209	314	428
	max	276	233	285	418	532

ASTM A194 Mechanical Properties of Nuts

This specification covers carbon, alloy and stainless steel nuts intended for use in high-pressure and/or high-temperature service. Unless otherwise specified, heavy hex nuts (ANSI B 18.2.2) shall be used. Nuts up to and including 1-inch nominal size shall be UNC Series Class 2B fit. Nuts over 1-inch nominal size shall be either UNC Series Class 2B fit or 8 UN Series Class 2B fit

GRADE	PROOF LOAD STRESS ksi	HARDNESS - BRINELL
2	150	159-352
2H	175	245-348
2HM	150	159-237
4	175	245-348
7	175	245-348
7M	150	159-237
8	80	126-300
8M	80	126-300

ASTM A563 Mechanical Properties

GRADE	STYLE	SIZE (in)	PROOF LOAD, ksi		HARDNESS - BRINELL
			PLAIN	GALV	HB
A	HEX	1/4 - 1.1/2	90	68	116-302
	HEAVY HEX	1/4 - 4	100	75	116-302
B	HEAVY HEX	1/4 - 1	133	100	121-302
	HEAVY HEX	1.1/8 - 1.1/2	116	87	121-302
C/C3	HEAVY HEX	1/4 - 4	144	144	143-352
D	HEAVY HEX	1/4 - 4	150	150	248-352
DH/DH3	HEAVY HEX	1/4 - 4	175	150	248-352

SAE J995

SAE J995 covers the mechanical and chemical requirements for inch series nuts in three grades used in automotive and related industries in sizes to 1-1/2” inclusive.

J995 Mechanical Properties

Grade	Nominal Size, inches	Proofload, UNC and UN 8 Threads, psi	Rockwell Hardness
2	1/4 thru 1-1/2	90,000	C32 Max
5	1/4 thru 1	120,000	C32 Max
5	Over 1 thru 1-1/2	105,000	C32 Max
8	1/4 thru 5/8	150,000	C24-C32
	Over 5/8 thru 1	150,000	C26-C34
	Over 1 thru 1-1/2	150,000	C26-C36
*Values listed are not normally applicable to lock, jam, slotted, castle, heavy or thick nuts.

J995 Chemical Requirements

Grade	Carbon, %	Phosphorus, %	Manganese, %	Sulfur, %
2	0.47 max	0.120 max	-	0.15 max
5	0.55 max	0.050 max	0.30 min	0.15 max
8	0.55 max	0.040 max	0.30 min	0.05 max

J995 Tensile Stress Area

Thread, UNC	UNC Stress Area, sq inches	Thread, 8TPI	8 TPI Stress Area, sq inches
1/2-13	0.1419
5/8-11	0.226
3/4-10	0.334
7/8-9	0.462
1-8	0.606	1-8	0.606
1-1/8-7	0.763	1-1/8-8	0.790
1-1/4-7	0.969	1-1/4-8	1.000
1-3/8-6	1.155	1-3/8-8	1.233
1-1/2-6	1.405	1-1/2-8	1.492
To calculate individual nut proofload value, simply multiply the tensile stress area by the appropriate psi proofload value.

PLEASE DO NOT RELY ON THE INFORMATION PROVIDED, TROJAN DOES NOT IMPLY WARRANTY OR GIVE ANY GUARANTEES THE INFORMATION PROVIDED ABOVE OR ANYWHERE ON THIS SITE IS ACCURATE. YOU MUST INDEPENDENTLY VERIFY THE INFORMATION - THIS IS YOUR RESPONSIBILITY

Trojan Special Fasteners Ltd. | Midlands Fastener Manufacturer | Nuts and Bolts

+44 (0) 121 789 8586 | +44 (0) 121 789 8006

Fastener Grades

Which nuts can come in higher tensile grades?

If a customer requests a fastener to a grade that is not specified within it's dimensional specification, it will be made to within the hardness limits below.

ISO 898-2:2012

DIN267 part 3: 1967 Mechanical Properties of Nuts

BS1083 - Mechanical Properties of Finished Steel Hexagon Nuts

Comparison of strength Grades between BS1768 and BS970

British Fastener Grades

BS3692 - Mechanical Properties of Finished Steel Hexagon Nuts

EN ISO 898-1:2013

EN ISO 898-5:2012 Mechanical Properties of fasteners made of steel

ASTM A194 Mechanical Properties of Nuts

ASTM A563 Mechanical Properties

SAE J995

J995 Mechanical Properties

J995 Chemical Requirements

J995 Tensile Stress Area

Trojan Special Fasteners Ltd. | Midlands Fastener Manufacturer | Nuts and Bolts

+44 (0) 121 789 8586 | +44 (0) 121 789 8006

Fastener Grades

Which nuts can come in higher tensile grades?

If a customer requests a fastener to a grade that is not specified within it's dimensional specification, it will be made to within the hardness limits below.

ISO 898-2:2012

DIN267 part 3: 1967 Mechanical Properties of Nuts

BS1083 - Mechanical Properties of Finished Steel Hexagon Nuts

Comparison of strength Grades between BS1768 and BS970

British Fastener Grades

BS3692 - Mechanical Properties of Finished Steel Hexagon Nuts

EN ISO 898-1:2013

EN ISO 898-5:2012 Mechanical Properties of fasteners made of steel

ASTM A194 Mechanical Properties of Nuts

ASTM A563 Mechanical Properties

SAE J995

J995 Mechanical Properties

J995 Chemical Requirements

J995 Tensile Stress Area

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