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 Clamp Load?
Clamp load is an important aspect of engineering and construction, as it
determines the amount of force that is applied to a fastener to hold two
or more objects together. So for example if you were joining together two
components and put a bolt through them and used a nut to bring the bolt
under tension, then the bolt stretches like a spring and applies a clamp
load to the joint. The clamp load is measured in units of
force such as pounds or newtons, and it is crucial to be aware of the
clamp load requirements of a specific application to ensure that the
chosen fastener can withstand the required load.
The clamp load of a fastener is determined by several factors, including
the size, material, and thread pitch of the fastener. Larger fasteners are
able to withstand more clamp load than smaller fasteners, and stronger
materials such as steel can withstand more clamp load than weaker
materials such as plastic. The thread pitch, or distance between threads,
also plays a role in determining the clamp load of a fastener. Fine thread
fasteners have a higher clamp load capacity than coarse thread fasteners
of the same size and material.
Another important factor to consider when assessing fastener clamp load is
the coefficient of friction. This coefficient describes the amount of
resistance a surface exerts on an object trying to move across it.
Therefore, the coefficient of friction can affect the clamp load in a
fastener as it will affect the amount of force required to move the
objects that the fastener is holding together.
It is important to select the appropriate fastener for the specific
application and to be aware of the clamp load requirements. For example,
using a fastener with a lower clamp load than is required can result in
the fastener becoming loose or even failing, causing the objects it is
holding together to separate. On the other hand, using a fastener with a
higher clamp load than is required can result in damage to the threads or
even cracking of the objects being held together. Therefore, it is
important to consult with a fastener expert or to use a fastener selection
guide to ensure that the proper fastener is chosen for the specific
application.
In summary, fastener clamp load is an important measure of the amount of
force applied to a fastener to hold two or more objects together,
ultimately this is the best measure of joint integrity. It is crucial to
be aware of the clamp load requirements of a specific application and to
select the appropriate fastener to ensure that it can withstand the
required load. Factors such as the size, material, and thread pitch of the
fastener, as well as the coefficient of friction, all play a role in
determining the clamp load of a fastener. Consulting with a fastener
expert or using a fastener selection guide can help to ensure that the
proper fastener is chosen for the specific application.
What is Yield Strength?
The Yield Strength is defined as the amount of stress at which a predetermined amount of plastic (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
It has been shown that there is an approximately linear correlation between indentation hardness and yield strength as well as, more importantly, tensile strength for ferrous (nonaustenitic) hypoeuctoid (less than 0.8% carbon) steels. This means that it is relatively cost-effective and easy to perform non-destructive Rockwell testing of metals.
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.
When it comes to choosing the right nut for a specific application, it is important to understand the different types of nuts available, the different grades of internally threaded fasteners, and how they match up with the externally threaded fastener. At Trojan Special Fasteners Ltd, we understand the importance of selecting the correct nut for the right application and we are here to help you make the best choice for your needs.
One of the first things to consider when choosing a nut is the proof loading. Proof loading is the amount of force that a nut can withstand without breaking or deforming. This is a crucial factor to consider when selecting a nut for an application where high loads will be applied. For example, if a nut is being used in a heavy machinery application, it must be able to withstand the high loads that will be applied to it.
Another important factor to consider when choosing a nut is the application torque. This refers to the amount of torque that will be applied to the nut in order to properly secure it to the externally threaded fastener. The application torque must be matched to the nut in order to ensure that the nut is securely fastened and will not come loose under load.
When it comes to clamping force, it is important to understand that the nut and bolt or joint must be able to withstand the clamping force that will be applied to it. The clamping force is the amount of force that is applied to the nut and bolt or joint in order to keep it securely fastened. If the clamping force is not matched to the nut and bolt or joint, it can lead to failure.
Another important factor to consider when choosing a nut is the finish of the nut. The finish of the nut can affect the coefficient of friction between the nut and the externally threaded fastener. If the finish is smooth, the coefficient of friction will be low, which can lead to issues with nut loosening. If the finish is rough, the coefficient of friction will be high, which can help to keep the nut securely fastened.
The grade of the internally threaded fastener is also an important factor to consider when choosing a nut. The grade of the internally threaded fastener refers to the strength and hardness of the nut. The grade of the internally threaded fastener must match the grade of the externally threaded fastener in order to ensure that the nut and bolt or joint will be able to withstand the loads that will be applied to it.
When it comes to nut and bolt or joint failure, it is important to understand that this can occur due to a variety of factors. Nut and bolt or joint failure can occur due to improper torque, improper clamping force, or due to the nut and bolt or joint being mismatched in terms of grade. It is important to select the correct nut and bolt or joint for the application in order to avoid failure.
At Trojan Special Fasteners Ltd, we understand the importance of choosing the correct nut for the right application and we are here to help you make the best choice for your needs. We offer a wide range of nuts, bolts, and other fasteners to suit a variety of applications, and we are committed to providing our customers with the best products and service possible. Whether you need a nut for a heavy machinery application, or a bolt for a construction project, we have the right product for you. Contact us today to learn more about how we can help you choose the correct nut for the right application.
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 | - | - |
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