Stud bolts, hex bolts, nuts, washers and special fasteners in alloy steel, stainless steel, duplex and
nickel alloys — with the grades, strengths, thread sizes, markings and coatings you need to specify them.
Product Overview
The Bolting That Holds Every Joint
We supply stud bolts, hex bolts, heavy hex nuts, washers, socket head cap screws, threaded
rods, U bolts and foundation bolts — in alloy steel for flange bolting, in stainless steel
and duplex for corrosive service, and in nickel alloys, titanium and bronze for the most demanding
joints.
Studs and nuts are supplied as matched sets to the grade your flanges and piping class call for,
plain or coated. Every lot is marked with its grade and maker and supplied with a mill test
certificate to EN 10204 Type 3.1 or 3.2. When your project needs independent verification,
inspection by your nominated agency is carried out before dispatch.
Stud bolts and heavy hex nuts hold pressure joints together; the others fasten structures, equipment and pipe supports.
Flange boltingFull thread
Stud Bolt
A rod threaded along its full length, fitted with a heavy hex nut at each end. The standard bolting for pipe flanges and pressure vessels.
Standards
ASME B16.5 · B18.31.2
Grades
B7 · B7M · B16 · L7 · B8 · B8M
StructuresEquipment
Hex Bolt
A bolt with a hexagon head, part or fully threaded. Used for structural steelwork, machinery and equipment.
Standards
ASME B18.2.1 · ISO 4014 / 4017 · DIN 931 / 933
Grades
8.8 · 10.9 · A325 · A490 · A2 · A4
NutsMatched to the stud
Heavy Hex Nut
Thicker and wider across flats than a standard nut, to carry the full load of a high-strength stud. Supplied in the grade that matches the stud.
Standards
ASME B18.2.2 · ISO 4032 · DIN 934
Grades
2H · 2HM · 4 · 7 · 8 · 8M
Load spreadingLocking
Washers
Flat washers spread the load under the nut; spring, lock and hardened washers resist loosening and protect the joint face.
Standards
ASME B18.21.1 · B18.22.1 · F436 · DIN 125 / 127
Types
Flat · spring · hardened · lock
MachineryHigh strength
Socket Head Cap Screw
A cylindrical head driven by a hex key, for compact, high-strength joints in machines, dies and tools.
Standards
ISO 4762 · DIN 912 · ASME B18.3
Grades
12.9 · A2 · A4
Cut to lengthFull thread
Threaded Rod
Rod threaded end to end, in lengths of 1 to 3 m, cut on site into studs and hangers.
Standards
DIN 975 · ASTM A193 · ASME B18.31.3
Grades
B7 · B8 · B8M · 8.8 · A2 · A4
Pipe supports
U Bolt
A rod bent into a U and threaded at both ends, to clamp pipe to its supports.
Standards
MSS SP-58 · to drawing
Finish
Plain · galvanised · stainless
Anchoring
Foundation Bolt
J, L and headed anchor bolts cast into concrete to hold down columns, equipment and machinery.
Standards
ASTM F1554 · IS 5624
Grades
F1554 Gr. 36 · 55 · 105
Lifting
Eye Bolt
A forged bolt with a loop head, for lifting points on equipment and for rigging.
Standards
DIN 580 · ASME B18.15
Material
C15 · stainless A2 · A4
Measuring
How a Bolt and a Stud Are Measured
A bolt and a stud of the same length are not the same size: the length of each is measured in a different way. These are the dimensions to give on an enquiry.
Hex bolt (left) and stud bolt with two heavy hex nuts (right). The chamfered points at each end of the stud are not counted in its length.
d · nominal diameter
The outside diameter of the thread: M20, or 3/4" and so on.
L · length
Hex bolt: from under the head to the end. Stud bolt: along the thread, excluding the chamfered points, as ASME B16.5 specifies.
b · thread length
For part-threaded bolts. Stud bolts are threaded along their full length.
k, H & across flats
Head height, nut height, and the spanner size across the flats. Heavy hex nuts are about as high as the thread diameter.
For flange bolting, give the flange size, class and facing and we will work out the stud diameter, number and length. The bolt count and size for each flange are in the flange dimension chart.
Grades & Nuts
Every Stud Grade, With the Nut That Matches
A bolted joint is only as good as its weakest part, so each stud or bolt grade has a matching nut grade. Choose a family to see the pairs.
Alloy Steel Bolting for Pressure & High Temperature
ASTM A193 studs with A194 nuts are the standard bolting for flanges in refinery, chemical and power plant piping.
Studs & bolts
ASTM A193 · ASME SA193
Nuts
ASTM A194 · ASME SA194
Sour service
NACE MR0175 / ISO 15156
Stud grade
Material
Nut grade
Where it is used
A193 B7
Cr-Mo alloy steel (4140), quenched & tempered
A194 2H
General flange bolting, to about 450 °C.
A193 B7M
As B7, hardness limited to 235 HBW
A194 2HM
Sour service and hydrogen-cracking risk.
A193 B16
Cr-Mo-V alloy steel, quenched & tempered
A194 Gr. 4 or 7
High-temperature flange bolting, beyond the range of B7.
A193 B6
13 % chromium stainless (410)
A194 Gr. 6
Moderately corrosive and elevated-temperature service.
Low-Temperature Bolting
ASTM A320 studs are impact tested at low temperature, for cold climates, refrigeration and cryogenic plant.
Studs & bolts
ASTM A320 · ASME SA320
Nuts
ASTM A194, impact tested
Test
Charpy V-notch
Stud grade
Material
Nut grade
Where it is used
A320 L7
Cr-Mo alloy steel, impact tested at −101 °C
A194 Gr. 7 or 4
Low-temperature flange bolting.
A320 L7M
As L7, hardness limited
A194 Gr. 7M
Low-temperature sour service.
A320 L43
Ni-Cr-Mo alloy steel (4340)
A194 Gr. 7 or 4
Larger diameters at low temperature.
A320 B8 / B8M
Austenitic stainless, 304 / 316
A194 Gr. 8 / 8M
Cryogenic service, such as LNG.
Stainless Steel Fasteners
A193 B8 grades for pressure bolting, in Class 1 (solution treated) or the stronger Class 2 (strain hardened); F593 and ISO 3506 grades for general stainless fastening.
Pressure bolting
ASTM A193 B8 · A194 Gr. 8
General fasteners
ASTM F593 / F594
Metric
ISO 3506-1 / 3506-2
Stud / bolt grade
Material
Nut grade
Where it is used
A193 B8 Cl. 1 / Cl. 2
304 stainless
A194 Gr. 8
Stainless flanges in water and mild chemical service.
A193 B8M Cl. 1 / Cl. 2
316 stainless
A194 Gr. 8M
Chemical, coastal and marine flange bolting.
A193 B8T
321 stainless
A194 Gr. 8T
Stabilised grade for high temperature.
A193 B8C
347 stainless
A194 Gr. 8C
Stabilised grade for high temperature.
F593 Gr. 304 / 316
304 / 316 stainless
F594
General stainless bolts, screws and studs.
ISO 3506 A2-70
304 type stainless, 700 MPa
A2-70
Metric fasteners for general and food equipment.
ISO 3506 A4-70 / A4-80
316 type stainless, 700 / 800 MPa
A4-70 / A4-80
Marine and chemical environments.
Structural & General Engineering Fasteners
Carbon and alloy steel bolts graded by strength, for steel structures, machinery, anchoring and general fabrication.
Inch
ASTM A307 · F3125 · A563 · F436
Metric
ISO 898-1 · ISO 898-2
Indian
IS 1367 · IS 5624
Bolt grade
Material
Nut grade
Where it is used
A307 Gr. A / B
Low carbon steel
A563 Gr. A
General bolting; Gr. B for cast iron flanges.
F3125 A325
Medium carbon steel, quenched & tempered
A563 DH · A194 2H
High-strength structural steel connections.
F3125 A490
Alloy steel, quenched & tempered
A563 DH · A194 2H
Heavily loaded structural connections.
ISO 8.8
Carbon or alloy steel, quenched & tempered
Class 8
General engineering and machinery.
ISO 10.9
Alloy steel, quenched & tempered
Class 10
High-strength machinery and friction-grip joints.
ISO 12.9
Alloy steel, quenched & tempered
Class 12
Socket head cap screws and highly stressed joints.
F1554 Gr. 36 / 55 / 105
Carbon or alloy steel anchor rods
A563 · A194 2H
Foundation and anchor bolts in concrete.
Duplex & Special Alloy Fasteners
Studs and nuts machined from duplex and precipitation-hardening bar for seawater, offshore and high-temperature service. Nuts are made from the same grade as the stud.
Duplex bar
ASTM A276 · A479
Superalloy
ASTM A453
PH stainless
ASTM A564
Grade
Material
Nut grade
Where it is used
Duplex 2205
UNS S31803 / S32205
Same grade
Seawater and offshore flange bolting.
Super Duplex 2507
UNS S32750 / S32760
Same grade
Subsea, seawater and firewater systems.
A453 Gr. 660
Iron-nickel superalloy (A-286)
A453 Gr. 660
High-temperature turbine and exhaust bolting.
17-4PH (630)
Precipitation-hardening stainless, H1150
Same grade
Valve and pump bolting needing strength and corrosion resistance.
Nickel Alloy Fasteners
Bolts, studs and nuts for chemical, seawater and high-temperature service, machined from nickel-alloy bar.
Alloy
UNS
Bar specification
Where it is used
Monel 400
N04400
B164
Seawater and hydrofluoric acid service.
Monel K-500
N05500
B865
High-strength marine and subsea bolting.
Inconel 625
N06625
B446
Seawater and severe chemical service.
Inconel 718
N07718
B637
High-strength, high-temperature and sour-service bolting.
Hastelloy C276
N10276
B574
Wet chlorine and mixed acids.
Alloy 20
N08020
B473
Sulphuric acid service.
Titanium & Non-Ferrous Fasteners
Light, non-magnetic or non-sparking fasteners for seawater, electrical and special applications.
Material
UNS
Bar specification
Where it is used
Titanium Gr. 2
R50400
B348
Seawater and chemical equipment.
Titanium Gr. 5
R56400
B348
High strength at low weight.
Brass
C36000
B16
Electrical and decorative fasteners.
Silicon Bronze
C65100 / C65500
B98
Marine and electrical fasteners.
Aluminium Bronze
C63000
B150
Non-sparking and seawater fasteners.
Swipe the table sideways to see every column
Use the nut grade listed with each stud; a weaker nut can strip before the stud reaches its full load. Bar grades for machined fasteners are on the Round Bars page.
Strength
Strength by Grade and by Size
The grade sets how strong the material is; the size sets how much load one fastener carries. Both charts use the minimum values of the standard.
Minimum tensile strength
MPa · bolting grades
ISO 12.91220
ISO 10.9 · A4901040
B7 · B16 · L7860
ISO 8.8 · A325830
A4-80800
B8M Cl. 2760
A2-70700
B7M690
B8 · B8M Cl. 1515
A307 Gr. A415
Class 1 stainless studs are soft; where stainless bolting must carry a high load, Class 2 strain-hardened studs are used.
Breaking load of a class 8.8 bolt
kN · stress area × minimum tensile strength
M36678.1
M30465.6
M24293.0
M20203.4
M16125.6
M1267.4
M1046.4
Load grows with the square of the diameter: an M36 bolt carries about ten times the load of an M12. Every size is in the thread table below.
Grade
Specification
Size range
Tensile strength MPa
Yield strength, min MPa
Hardness, max HBW
ASTM pressure bolting
B7
ASTM A193
To 64 mm (2½")
860 min
720
321
B7M
ASTM A193
To 100 mm (4")
690 min
550
235
B16
ASTM A193
To 64 mm (2½")
860 min
725
321
L7
ASTM A320
To 64 mm (2½")
860 min
725
–
B8 · B8M Cl. 1
ASTM A193
All sizes
515 min
205
223
B8 Cl. 2
ASTM A193
To 20 mm (3/4")
860 min
690
321
B8M Cl. 2
ASTM A193
To 20 mm (3/4")
760 min
655
321
A453 Gr. 660 Cl. A
ASTM A453
All sizes
895 min
585
–
Structural & general
A307 Gr. A
ASTM A307
All sizes
415 min
–
–
A325
ASTM F3125
To 25 mm (1")
830 min
635
–
A490
ASTM F3125
All sizes
1040 – 1210
895
–
8.8
ISO 898-1
Over M16
830 min
660
–
10.9
ISO 898-1
All sizes
1040 min
940
–
12.9
ISO 898-1
All sizes
1220 min
1100
–
Stainless, ISO 3506
A2-70 · A4-70
ISO 3506-1
To M24
700 min
450
–
A4-80
ISO 3506-1
To M24
800 min
600
–
Swipe the table sideways to see every column
Larger sizes of B7 and A325 have lower minimum strengths; the value for your size is reported on the mill test certificate. Class 8.8 up to M16 has a minimum tensile strength of 800 MPa.
Markings
What the Stamp on a Fastener Means
Bolts, studs and nuts are stamped with their grade and the maker's mark, so the right parts can be checked on site. These are the markings you will see most.
1B722H38.8410.95A4-80
B7 · stud gradeStamped on one end of an ASTM A193 stud, with the maker's mark. B7M, B16, L7 and B8M are marked the same way.
2H · nut gradeStamped on the face of an ASTM A194 heavy hex nut. 2HM, 4, 7, 8 and 8M nuts are marked the same way.
8.8 · property classISO 898-1: 8 × 100 = 800 MPa nominal tensile strength; the second 8 means yield is 80 % of that, 640 MPa.
10.9 · property class1000 MPa nominal tensile strength, with yield at 90 %, 900 MPa. 12.9 follows the same rule.
A4-80 · stainlessISO 3506: A4 is 316-type stainless with molybdenum (A2 is 304-type); 80 means 800 MPa tensile strength.
Thread Tables
Thread Pitch, Spanner Size and Load
Coarse-thread sizes with their pitch, the across-flats spanner size of the nut, the tensile stress area and the minimum breaking load. Switch between metric bolts and inch stud bolts.
Showing metric coarse thread, ISO 261
Size
Pitchmm
Across flatsmm, ISO nut
Stress areamm²
Breaking loadclass 8.8, kN
Breaking loadclass 10.9, kN
M6
1.0
10
20.1
16.1
20.9
M8
1.25
13
36.6
29.3
38.1
M10
1.5
16
58.0
46.4
60.3
M12
1.75
18
84.3
67.4
87.7
M14
2.0
21
115
92.0
119.6
M16
2.0
24
157
125.6
163.3
M20
2.5
30
245
203.4
254.8
M22
2.5
34
303
251.5
315.1
M24
3.0
36
353
293.0
367.1
M27
3.0
41
459
381.0
477.4
M30
3.5
46
561
465.6
583.4
M33
3.5
50
694
576.0
721.8
M36
4.0
55
817
678.1
849.7
M39
4.0
60
976
810.1
1015.0
M42
4.5
65
1120
929.6
1164.8
M48
5.0
75
1470
1220.1
1528.8
M56
5.5
85
2030
1684.9
2111.2
M64
6.0
95
2680
2224.4
2787.2
Breaking load is calculated as stress area × minimum tensile strength: 800 MPa for class 8.8 up to M16 and 830 MPa above; 1040 MPa for class 10.9. Across flats to ISO 4032; some DIN sizes differ (M10: 17, M12: 19, M14: 22, M22: 32 mm).
Sizeinch
Threadsper inch
Series
Heavy hex nut AFinch · mm
Nut heightinch
Stress areamm²
Breaking loadB7, kN
1/2
13
UNC
7/8 · 22.2
31/64
91.5
78.7
5/8
11
UNC
1 1/16 · 27.0
39/64
145.8
125.4
3/4
10
UNC
1 1/4 · 31.8
47/64
215.5
185.3
7/8
9
UNC
1 7/16 · 36.5
55/64
298.1
256.3
1
8
UNC
1 5/8 · 41.3
63/64
391.0
336.2
1 1/8
8
8UN
1 13/16 · 46.0
1 7/64
509.7
438.3
1 1/4
8
8UN
2 · 50.8
1 7/32
645.2
554.8
1 3/8
8
8UN
2 3/16 · 55.6
1 11/32
795.5
684.1
1 1/2
8
8UN
2 3/8 · 60.3
1 15/32
962.6
827.8
1 3/4
8
8UN
2 3/4 · 69.9
1 23/32
1341.9
1154.1
2
8
8UN
3 1/8 · 79.4
1 31/32
1787.1
1536.9
Stud bolts for flanges use UNC thread up to 1" and the 8-thread series (8UN) above, as ASME B16.5 requires. B7 breaking load is stress area × 860 MPa, the minimum up to 2½".
Swipe the table sideways to see every column
Coatings
Coatings That Keep Bolts Working
A coating protects carbon and alloy steel bolting from corrosion, and some coatings also make the joint easier to tighten and to take apart.
Plain
Plain & black
As heat treated, with a dark oxide surface and a light oil. The standard supply condition of B7 studs.
Best forIndoor and insulated joints, and bolting that will be coated later
Zn
Zinc electroplated
A thin, bright zinc layer with a clear or coloured passivation. Mild protection for indoor use.
StandardASTM F1941 · ISO 4042
HDG
Hot-dip galvanised
Dipped in molten zinc for a thick, durable coating. Nuts are tapped oversize after galvanising to fit.
StandardASTM F2329 · A153 · ISO 10684
Zn-Ni
Zinc-nickel
An electroplated zinc-nickel alloy that lasts several times longer than plain zinc in salt spray.
StandardASTM B841
PTFE
PTFE fluoropolymer
A fluoropolymer coat over a phosphate base, usually blue or green. Resists corrosion and makes tightening and removal easier.
Best forOffshore, coastal and chemical plant flange bolting
Phos
Phosphate & oil
A matt grey zinc or manganese phosphate, sealed with oil. Mild protection and a good base for other coatings.
StandardASTM F1137
High-strength fasteners of about 1000 MPa and above can be embrittled by electroplating; for these, mechanical or non-electrolytic coatings are used. The swatches are drawings that suggest each coating.
Selection
Which Fastener for Which Joint?
A starting point for choosing the grade. The flange material, service temperature and environment decide the bolting; tell us those and we will quote the right sets.
Joint
Typical choice
Why
Carbon steel flanges, general service
A193 B7 · A194 2H
The standard high-strength flange bolting.
Sour service, NACE MR0175
A193 B7M · A194 2HM
Hardness limited to resist sulphide stress cracking.
Low temperature
A320 L7 · A194 Gr. 7
Impact tested for toughness in the cold.
Cryogenic, LNG
A320 B8 / B8M · A194 8 / 8M
Austenitic stainless stays tough at very low temperature.
High temperature
A193 B16 · A453 Gr. 660
Keep their strength and resist relaxation when hot.
Stainless flanges, strong joint
A193 B8M Cl. 2 · A194 8M
Strain hardened for high load, 316 for corrosion.
Seawater and offshore
Duplex · Super duplex · Monel K-500 · PTFE-coated B7
Resist chloride corrosion in splash and immersion.
Structural steel connections
F3125 A325 / A490 · ISO 8.8 / 10.9
High-strength, pre-tensioned structural bolting.
General machinery
ISO 8.8 · 10.9 · 12.9
Strength graded to the load.
General stainless assemblies
ISO A2-70 · A4-80
Corrosion-resistant fasteners for plant and equipment.
Foundations and anchors
F1554 · IS 5624, galvanised
Anchor rods cast into concrete, protected against corrosion.
Cast iron flanges
A307 Gr. B
Low strength, so it cannot overload a brittle flange.
Swipe the table sideways to see every column
This guide is for orientation only. Bolting selection depends on the full service conditions and the governing piping or structural code, and remains the responsibility of the design engineer.
Testing & Documents
Tested, Traceable & Documented
Every lot is traceable to its heat and leaves with its mill test certificate. These tests are arranged when your order calls for them.
What is the difference between B7 and B7M stud bolts?
Both are ASTM A193 chromium-molybdenum alloy steel studs. B7M is tempered to a lower strength with a maximum hardness of 235 HBW and every stud is hardness tested, so it is suitable for sour service to NACE MR0175. B7 is stronger, with a minimum tensile strength of 860 MPa up to 64 mm diameter, and is the standard stud for general flange bolting. B7M is used with 2HM nuts, and B7 with 2H nuts.
What does a property class such as 8.8 or 10.9 mean?
It is the ISO 898-1 strength class stamped on the bolt head. The first number times 100 is the nominal tensile strength in MPa, and the second number is the ratio of yield to tensile strength. So 8.8 means a nominal tensile strength of 800 MPa and a yield of 80 percent of that, 640 MPa; 10.9 means 1000 MPa and 900 MPa. See the markings.
How is the length of a stud bolt measured?
For flange stud bolts to ASME B16.5, the length is measured along the threaded length, excluding the chamfered points at each end. The length of a hex bolt is measured from the underside of the head to the end of the bolt. See the drawing.
What is the difference between A2 and A4 stainless steel fasteners?
Under ISO 3506, A2 is an austenitic stainless steel of the 304 type, and A4 contains molybdenum, like type 316, for better resistance to chlorides and seawater. The number after it is the strength: 70 means 700 MPa tensile strength and 80 means 800 MPa.
Can hot-dip galvanised bolts be used with ordinary nuts?
No. Hot-dip galvanising adds a thick zinc layer to the bolt thread, so galvanised bolts need nuts that are tapped oversize after galvanising. Bolts and nuts should be supplied as galvanised sets. See the coatings.
What documents are supplied with fasteners?
Fasteners are supplied with a mill test certificate to EN 10204 Type 3.1 or 3.2, traceable to the heat or lot number, with the mechanical and hardness test results and any coating reports ordered. When third-party inspection is called for, the agency's inspection release note is included. More on our quality & inspection page.
Complete the Joint
Everything That Goes With the Bolting
Flanges, pipe, fittings and valves in matching grades, so every joint comes from one supplier with one set of documents.
Send the fastener type, size, grade and coating, or your flange list. We will confirm availability and quote matched sets, with the mill test certificate and inspection you need.
