Fastener Grades
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:
Fp = 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.
Rm = 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 | ||||||||||
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 | |||
min. | 400 | 420 | 500 | 520 | 600 | 800 | 830 | 900 | 1040 | 1220 | ||
2 | Lower proof stress ReL ᵈ, MPa | nom. ᶜ | 240 | - | 300 | - | - | - | - | - | - | - |
min. | 240 | - | 300 | - | - | - | - | - | - | - | ||
3 | Yield strength, Rp0.2, MPa | nom. ᶜ | - | - | - | - | - | 640 | 640 | 720 | 900 | 1080 |
min. | - | - | - | - | - | 640 | 660 | 720 | 940 | 1100 | ||
4 | Yield strength at 0.0048 d for whole screw, Rpf, MPa | nom. ᶜ | - | 320 | - | 400 | 480 | - | - | - | - | - |
min. | - | 340ᵉ | - | 420ᵉ | 480ᵉ | - | - | - | - | - | ||
5 | Proof stress, Spᶠ, MPa | nom. | 225 | 310 | 280 | 380 | 440 | 580 | 600 | 650 | 830 | 970 |
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 |
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 |
max. | 209ᵍ | 238 | 304 | 318 | 342 | 361 | 414 | |||||
12 | Rockwell hardness, HRB | min. | 67 | 71 | 79 | 82 | 89 | - | ||||
max. | 95,0ᵍ | 99,5 | - | |||||||||
Rockwell hardness, HRC | min. | - | 22 | 23 | 28 | 32 | 39 | |||||
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 | ||||||
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