Heavy Series Flange Bolts
EN 1665 (DIN 6921) · M5 – M20 · 8.8 / 10.9 / A2-70The general-purpose flange bolt. Since EN 1665 its hexagon matches an ISO 4014 hex bolt, so the same spanners fit. Supplied with a plain or serrated flange.
DIN 6921 & EN 1665 Bolts, Plain and Serrated: Manufacturer & Supplier
A hex flange bolt is a hexagon head bolt with a round flange formed in one piece under the head. The flange works as a built-in washer. It spreads the clamp load, bridges oversized and slotted holes, and removes a loose part from the assembly line.
Exotic Alloy manufactures hex flange bolts in Mumbai, India. We make the heavy series to EN 1665 (which replaced DIN 6921), the small series to ISO 4162 and ISO 15071, and inch flange screws to IFI-111. Heads are cold forged with the flange and, on request, the serrations formed in the die. We supply across India and export to South Africa, the Gulf, Europe and the Americas.
Ready Stock & Custom Sizes
Common EN 1665 and DIN 6921 sizes in 8.8 and 10.9 zinc flake and in A2-70 stainless ship from stock. Serrated flanges, the ISO 4162 small series, inch screws, special lengths and exotic alloys are made to order in 7 to 15 business days.
M5 – M20 | ¼ – ¾″
Plain or serrated flange
Heavy & small series
Coarse & fine, UNC & UNF
Partial & full thread
Hex flange bolt at a glance
- Head
- Hexagon with integral round flange; flange larger than an ISO 7089 washer
- Underside
- Plain bearing face or radial serrations (locking)
- Standards
- EN 1665 / DIN 6921, ISO 4162, ISO 15071, ISO 15072, IFI-111, ASME B18.2.1
- Grades
- 8.8, 9.8, 10.9, 12.9 (fine), A2-70; SAE Grade 5 / 8
- Installed
- With a spanner or socket; no separate washer
- Related
- Hex bolts, washers, flange nuts
Hex Flange Bolt Specification
The range we manufacture and supply.
StandardsDIN EN 1665 heavy series (replaces DIN 6921); ISO 4162 and ISO 15071 small series; ISO 15072 fine pitch; IFI-111 and ASME B18.2.1 inch hex flange screws; IS 1367 properties
Size rangeEN 1665 / DIN 6921 M5 to M20; ISO 4162 M5 to M16; inch ¼″ to ¾″. Partial or full thread; larger sizes made to drawing
ThreadISO metric coarse 6g; metric fine to ISO 15072 (M8×1 to M16×1.5); UNRC / UNRF class 2A for inch; left-hand on request; rolled
FlangePlain bearing face, or radial serrations for locking; conical or rounded flange top; formed underhead fillet
GradesISO 898-1 classes 8.8, 9.8 (ISO 15071), 10.9, 12.9 (ISO 15072, by agreement); ISO 3506-1 A2-70, A4-70 on request; SAE J429 Grade 5 / 8; ASTM A449, A354 BD, F593
MaterialsMedium carbon and boron steel (8.8); Cr-Mo alloy steel 4135 / 4140 (10.9, 12.9); stainless 304, 316; duplex 2205 / 2507; Inconel 625 / 718; Monel 400 / K-500; titanium Gr. 2 / 5
FinishZinc flake (ISO 10683), zinc or zinc-nickel electroplate with baking, phosphate and oil, black oxide, plain, passivated stainless
CertificationEN 10204 3.1 with heat number, tensile / proof load and hardness; 3.2 by TUV, DNV, Lloyd's, BV or SGS; PMI for stainless and alloys
MarkingProperty class and manufacturer's mark on the hex top or the flange; A2-70 for stainless; SAE grade lines (3 for Grade 5, 6 for Grade 8) on inch screws
PackingBoxes or bags by size and length with label showing standard, grade, size, quantity and heat number; export cartons on pallets
Types of Hex Flange Bolts We Manufacture
Two head series, two flange styles and an inch range. Each card names the standard to put on your order.
Small Series Flange Bolts
ISO 4162 / ISO 15071 · M5 – M16 · 8.8 / 9.8 / 10.9A smaller hexagon (13 mm for M10, 15 mm for M12) and a slightly smaller flange. Saves weight and space, so it is common in engines, gearboxes and car bodies.
Serrated Flange Bolts
Locking teeth on the flange undersideRadial teeth bite into the clamped surface and resist loosening under vibration, without a lock washer or adhesive. Usually made in 10.9 or SAE Grade 8 so that the teeth are harder than the joint.
Fine Thread Flange Bolts
ISO 15072 · M8×1 – M16×1.5Small series flange bolts with metric fine threads for thin-walled and high-strength joints, including class 12.9 by agreement.
Inch Hex Flange Screws
IFI-111 / ASME B18.2.1 · ¼ – ¾″ · SAE Grade 5 / 8UNC and UNF threads, class 2A, with a full or indented head and three standard fillet styles. Plain or serrated, in Grade 5, Grade 8 and F593 stainless.
Stainless & Exotic Alloy Flange Bolts
A2 / A4 · duplex · Inconel · Monel · titaniumEN 1665 or ISO 4162 heads in corrosion-resistant alloys for food plants, chemical and marine equipment, and exhaust systems.
Flange bolt or hex bolt with washer?
| M12 example | Flange bolt (EN 1665) | Hex bolt (ISO 4014) + ISO 7089 washer |
|---|---|---|
| Parts per joint | 1 (bolt), plus nut if through-bolted | 2 or 3 (bolt, washer, nut) |
| Bearing outer diameter | Flange 26.6 mm max | Washer 24 mm |
| Spanner | 18 mm | 18 mm |
| Locking option | Serrated flange | Separate locking element needed |
| Assembly | No washer to drop or forget; suits automated lines | Washer can be omitted or misplaced |
| Size range | M5 to M20 (EN 1665) | M1.6 to M64 (ISO 4014) |
Hex Flange Bolt Dimensions: EN 1665, ISO 4162 & IFI-111
Metric dimensions from DIN EN 1665:1998 and ISO 4162, inch dimensions from IFI-111 (2002). The last tab shows how the hexagon differs between the series and from the withdrawn DIN 6921.
| Size | Pitch P | dc max flange dia. | c min flange edge | k max head height | s across flats | e min across corners | ds min shank | b l ≤ 125 / ≤ 200 / > 200 |
|---|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 11.8 | 1 | 5.8 | 8 | 8.71 | 4.82 | 16 / – / – |
| M6 | 1 | 14.2 | 1.1 | 6.6 | 10 | 10.95 | 5.82 | 18 / – / – |
| M8 | 1.25 | 18 | 1.2 | 8.1 | 13 | 14.26 | 7.78 | 22 / 28 / – |
| M10 | 1.5 | 22.3 | 1.5 | 10.4 | 16 | 17.62 | 9.78 | 26 / 32 / – |
| M12 | 1.75 | 26.6 | 1.8 | 11.8 | 18 | 19.86 | 11.73 | 30 / 36 / – |
| M14 | 2 | 30.5 | 2.1 | 13.7 | 21 | 23.15 | 13.73 | 34 / 40 / – |
| M16 | 2 | 35 | 2.4 | 15.4 | 24 | 26.51 | 15.73 | 38 / 44 / 57 |
| M20 | 2.5 | 43 | 3 | 18.9 | 30 | 33.23 | 19.67 | 46 / 62 / 65 |
Dimensions in mm. dc is the flange diameter, c the minimum flange thickness at its edge, and k the overall head height including the flange. b is the thread length for nominal lengths up to 125 mm, 125 to 200 mm, and over 200 mm.
| Size | Pitch P | dc max flange dia. | c min flange edge | k max head height | k′ min wrenching height | s across flats | e min across corners | b l ≤ 125 |
|---|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 11.4 | 1 | 5.6 | 2.8 | 7 | 7.44 | 16 |
| M6 | 1 | 13.6 | 1.1 | 6.8 | 3.4 | 8 | 8.56 | 18 |
| M8 | 1.25 | 17 | 1.2 | 8.5 | 4.2 | 10 | 10.80 | 22 |
| M10 | 1.5 | 20.8 | 1.5 | 9.7 | 5.7 | 13 | 14.08 | 26 |
| M12 | 1.75 | 24.7 | 1.8 | 11.9 | 6.1 | 15 | 16.32 | 30 |
| M14 | 2 | 28.6 | 2.1 | 12.9 | 7.1 | 18 | 19.68 | 34 |
| M16 | 2 | 32.8 | 2.4 | 15.1 | 8.7 | 21 | 22.58 | 38 |
Dimensions in mm. k′ is the minimum wrenching height of the hexagon. ISO 15071 uses the same flange and head sizes. Note that DIN EN 1662, the European small series, lists a 16 mm hexagon for M12, not 15 mm; please state which standard your drawing uses.
| Size | Threads / in UNC / UNF | Wrench F basic (max / min), in | Across corners G max / min, in | Flange B max, in | Bearing B1 min, in | Flange edge K min, in | Head H max, in | Thread LT L ≤ 6″, in |
|---|---|---|---|---|---|---|---|---|
| 1/4″ | 20 / 28 | 3/8″ (0.375 / 0.367) | 0.433 / 0.409 | 0.56 | 0.48 | 0.04 | 0.28 | 0.750 |
| 5/16″ | 18 / 24 | 1/2″ (0.500 / 0.489) | 0.577 / 0.548 | 0.68 | 0.60 | 0.05 | 0.32 | 0.875 |
| 3/8″ | 16 / 24 | 9/16″ (0.562 / 0.551) | 0.650 / 0.618 | 0.81 | 0.73 | 0.06 | 0.39 | 1.000 |
| 7/16″ | 14 / 20 | 5/8″ (0.625 / 0.612) | 0.722 / 0.685 | 0.93 | 0.85 | 0.07 | 0.46 | 1.125 |
| 1/2″ | 13 / 20 | 3/4″ (0.750 / 0.736) | 0.866 / 0.825 | 1.07 | 0.98 | 0.08 | 0.51 | 1.250 |
| 9/16″ | 12 / 18 | 13/16″ (0.812 / 0.798) | 0.938 / 0.895 | 1.19 | 1.10 | 0.09 | 0.57 | 1.375 |
| 5/8″ | 11 / 18 | 15/16″ (0.938 / 0.922) | 1.083 / 1.034 | 1.33 | 1.23 | 0.10 | 0.62 | 1.500 |
| 3/4″ | 10 / 16 | 1-1/8″ (1.125 / 1.100) | 1.299 / 1.234 | 1.59 | 1.47 | 0.11 | 0.73 | 1.750 |
IFI-111 hex flange screws, dimensions in inches. B is the flange diameter and B1 the minimum bearing circle, sized so that the clamped surface sees at most 20,500 psi at 75 % of the Grade 5 fine-thread proof load. K is the minimum flange thickness at B1 and H the head height. The top of the head may be full or indented.
| Size | ISO 4014 hex bolt s, mm | DIN 6921 withdrawn, s mm | EN 1665 heavy s, mm | ISO 4162 small s, mm | Flange dc max EN 1665 / ISO 4162 | ISO 7089 washer outside dia. |
|---|---|---|---|---|---|---|
| M5 | 8 | 8 | 8 | 7 | 11.8 / 11.4 | 10 |
| M6 | 10 | 10 | 10 | 8 | 14.2 / 13.6 | 12 |
| M8 | 13 | 13 | 13 | 10 | 18 / 17 | 16 |
| M10 | 16 | 15 | 16 | 13 | 22.3 / 20.8 | 20 |
| M12 | 18 | 16 | 18 | 15 | 26.6 / 24.7 | 24 |
| M14 | 21 | 18 | 21 | 18 | 30.5 / 28.6 | 28 |
| M16 | 24 | 21 | 24 | 21 | 35 / 32.8 | 30 |
| M20 | 30 | 27 | 30 | – | 43 / – | 37 |
Across-flats sizes in mm. Bold DIN 6921 values are the ones EN 1665 changed, so old DIN 6921 bolts from M10 upward need a different spanner. The flange diameters of DIN 6921 and EN 1665 are the same.
Why the Flange Matters: Bearing Area & Surface Pressure
The clamp load passes through the ring between the clearance hole and the edge of the bearing face. A bigger ring means lower pressure on the joint, less embedding and less loss of preload over time.
Bearing area and pressure, EN 1665 flange bolts
| Size | Clearance hole ISO 273 medium, mm | Flange dc max EN 1665, mm | Flange bearing area mm², approx. | Hex head bearing area at most, mm² | Ratio flange / hex, at least | Preload FM 10.9 μ 0.14, kN | Pressure under flange MPa, approx. |
|---|---|---|---|---|---|---|---|
| M5 | 5.5 | 11.8 | 86 | 27 | 3.2× | 9.4 | 110 |
| M6 | 6.6 | 14.2 | 124 | 44 | 2.8× | 13.2 | 107 |
| M8 | 9 | 18 | 191 | 69 | 2.7× | 24.3 | 127 |
| M10 | 11 | 22.3 | 296 | 106 | 2.7× | 38.7 | 131 |
| M12 | 13.5 | 26.6 | 413 | 111 | 3.7× | 56.4 | 137 |
| M14 | 15.5 | 30.5 | 542 | 158 | 3.4× | 77.4 | 143 |
| M16 | 17.5 | 35 | 722 | 212 | 3.4× | 106.6 | 148 |
| M20 | 22 | 43 | 1072 | 327 | 3.2× | 166.5 | 155 |
Our calculation. Flange area = π/4 (dc² − dh²) using dc max, so the real value is a little lower. The hex head figure uses a circle the size of the across-flats dimension, so the real hex bearing area is smaller still. Pressure is the class 10.9 assembly preload from the torque table divided by the flange area. Check it against the permissible surface pressure of the clamped material (VDI 2230 lists values), especially for aluminium, plastics and thin sheet.
Hex Flange Bolt Grades & Property Classes
The flange standards name a short list of classes. Other grades are made by agreement, and the certificate states the grade supplied.
| Grade / class | Standard | Tensile min | Yield min | Hardness | Where it applies |
|---|---|---|---|---|---|
| 8.8 | ISO 898-1 | 800 MPa (≤ M16) / 830 MPa | 640 / 660 MPa | 22–32 / 23–34 HRC | EN 1665, ISO 4162: the general-purpose flange bolt |
| 9.8 | ISO 898-1 | 900 MPa | 720 MPa | 28–37 HRC | ISO 15071 small series, up to M16 |
| 10.9 | ISO 898-1 | 1040 MPa | 940 MPa | 32–39 HRC | EN 1665, ISO 4162: automotive and machinery; most serrated flange bolts |
| 12.9 | ISO 898-1 | 1220 MPa | 1100 MPa | 39–44 HRC | ISO 15072 fine pitch, M8–M16, by agreement |
| A2-70 (A4-70 on request) | ISO 3506-1 | 700 MPa | 450 MPa | — | EN 1665, ISO 4162 stainless |
| SAE J429 Grade 5 | SAE J429 | 120 ksi (827 MPa) | 92 ksi (634 MPa) | 25–34 HRC | Inch flange screws, ¼–1″ |
| SAE J429 Grade 8 | SAE J429 | 150 ksi (1034 MPa) | 130 ksi (896 MPa) | 33–39 HRC | Inch flange screws, the usual serrated grade |
| ASTM A449 Type 1 | ASTM A449 | 120 ksi (827 MPa) | 92 ksi (634 MPa) | 25–34 HRC | Inch, ¼–1″ |
| ASTM A354 BD | ASTM A354 | 150 ksi (1034 MPa) | 130 ksi (896 MPa) | 33–39 HRC | Inch, high strength |
| F593 Group 1 / 2, CW1 | ASTM F593 | 100–150 ksi | 65 ksi (448 MPa) | — | Inch 304 / 316 stainless, ¼–⅝″ |
Serrations need hardness. Teeth only lock if they are harder than the surface they bite into. That is why serrated flange bolts are usually 10.9 or SAE Grade 8. Serrated A2-70 bolts work on softer metals, but they lose much of their effect against hardened steel.
Hex Flange Bolt Materials & Alloy Grades
Every grade links to its datasheet on this site.
Special stainless
904L · Nitronic 60 · A-286904L for acids, Nitronic 60 against galling, and A-286 for strength in hot exhaust and turbine parts.
Duplex 2205
S32205 / S31803About twice the yield strength of 316, with resistance to chloride stress corrosion cracking.
Exotic alloy flange bolts: minimum properties of the bar we make them from
| Alloy | UNS | Condition supplied | Tensile min MPa | Yield 0.2 % min MPa | Elongation % | Why it is chosen for hex bolts |
|---|---|---|---|---|---|---|
| Inconel 625 | N06625 | Solution annealed (Grade 1) | 827 | 414 | 30 | Seawater, sour gas, cryogenic to 980 °C oxidation; subsea flange bolting |
| Inconel 718 | N07718 | Solution treated + aged (AMS 5662) | 1240 | 1035 | 12 | Highest strength to 650 °C; turbine and wellhead bolting |
| Monel 400 | N04400 | Hot-finished annealed | 517 | 207 | 35 | Seawater, hydrofluoric acid, no chloride SCC; marine and valve bolting |
| Monel K-500 | N05500 | Age hardened (AMS 4676) | 960 | 690 | 18 | Monel 400 corrosion resistance with three times the yield; pump shafts, subsea |
| Hastelloy C-276 | N10276 | Solution annealed (ASTM B574) | 690 | 283 | 40 | Wet chlorine, hot acids, mixed oxidising / reducing media; chemical reactors |
| Incoloy 825 | N08825 | Annealed (ASTM B425) | 586 | 241 | 30 | Sulphuric and phosphoric acid, sour gas (NACE MR0175); pickling plant |
| Duplex 2205 | S32205 | Solution annealed | 655 | 450 | 25 | Twice the yield of 316 with chloride SCC resistance; offshore topsides |
| Super Duplex 2507 | S32750 | Solution annealed | 750 | 550 | 15 | PREN > 40; seawater and desalination bolting |
| Titanium Grade 5 | R56400 | Annealed (ASTM B348) | 895 | 828 | 10 | Half the weight of steel, immune to seawater; aerospace and chemical |
| A-286 | S66286 | Solution treated + aged | — | — | — | Iron-base superalloy for 650 °C bolting; on request with certified values |
Bar minimums from the linked datasheets for the supply condition shown. Exotic alloy flange bolts are certified to the material specification, not to an ISO 898-1 property class.
How Our Hex Flange Bolts Are Made
The flange and the hexagon are forged from one slug, so there is no joint between head and washer face.
1
Wire & bar
Spheroidize-annealed carbon, boron or Cr-Mo wire, received by heat with mill certificates. Stainless and exotic alloys come from certified bar.
2
Cold forging the head
A multi-station header upsets a large round head, then forms the hexagon above a full-diameter flange. Serrations, when ordered, are formed by the same die. Large sizes and exotic alloys are hot forged.
3
Trimming & pointing
The hexagon is trimmed where the design calls for it, the point is formed, and flange diameter, edge thickness and bearing-face runout are checked.
4
Thread rolling
Threads rolled to 6g, or to UNRC / UNRF class 2A for inch screws.
5
Quench & temper
Protective-atmosphere hardening and tempering to 22 to 32 HRC for 8.8 and 32 to 39 HRC for 10.9, with decarburization control at the flange edge and thread.
6
Finishing
Zinc flake, baked electroplate, phosphate and oil or black oxide for steel; passivation for stainless.
7
Testing
Hardness, wedge tensile and proof load per lot; dimensions and thread gauging; serration form checked against the drawing.
Finishes for flange bolts
| Finish | Specification | Corrosion | Suitable for | Notes |
|---|---|---|---|---|
| Zinc flake | ISO 10683 / ASTM F1136 | 600 to 1000 h salt spray | 8.8, 10.9, 12.9 | The usual automotive finish; no hydrogen embrittlement; controlled friction with top coat |
| Zinc-nickel | ISO 19598 / ASTM B841 | High | 8.8, 10.9 | Electroplated; baked after plating for 10.9 and above |
| Zinc electroplate | ISO 4042 / ASTM F1941 | Moderate | 8.8; 10.9 only with baking | Low cost; serration tips may show wear on assembly |
| Phosphate & oil | ISO 9717 | Indoor, oiled | All classes | Consistent friction for torque-controlled assembly |
| Black oxide | Thermal or chemical black, oiled | Indoor | All classes | Appearance and light protection |
| Passivated | ASTM A967 / A380 | Full stainless resistance | A2, A4, F593, duplex | Restores the passive film after forging and rolling |
Hex Flange Bolt Torque & Preload
Guide values by the VDI 2230 method, coarse thread, at 90 % of minimum yield. The bearing face is taken as the full flange (dc max) over an ISO 273 medium clearance hole. A flange bolt needs more torque than a hex bolt for the same preload, because the flange has a larger friction radius.
Preload & torque calculator
FM = 0.9 · Rp0.2 · A0 / √(1 + 3[2 (d2/d0)(P/πd2 + 1.155 μ)]²); MA = FM(0.16 P + 0.58 d2 μ + μ DKm/2), DKm = (dc + dh)/2. Plain flanges only: serrated flanges have much higher underhead friction.
Result for M12 class 10.9
145
N·m assembly torque
(107 lbf·ft)
56.4
kN assembly preload
(12.7 kip)
Stress area As:84.3 mm²
Min. yield Rp0.2:940 MPa
Flange dc / clearance hole:26.6 / 13.5 mm
Pressure under flange:137 MPa
Min. breaking load:87.7 kN
Torque table, EN 1665, μ = 0.14, 90 % of Rp0.2
| Size | Series | FM 8.8 kN | MA 8.8 N·m | FM 10.9 kN | MA 10.9 N·m | Hex bolt MA 8.8 ISO 4014, N·m |
|---|---|---|---|---|---|---|
| M5 | EN 1665 | 6.4 | 7.0 | 9.4 | 10 | 6.2 |
| M6 | EN 1665 | 9.0 | 12 | 13.2 | 17 | 11 |
| M8 | EN 1665 | 16.5 | 29 | 24.3 | 42 | 26 |
| M10 | EN 1665 | 26.3 | 56 | 38.7 | 83 | 50 |
| M12 | EN 1665 | 38.4 | 98 | 56.4 | 145 | 87 |
| M14 | EN 1665 | 52.7 | 156 | 77.4 | 229 | 139 |
| M16 | EN 1665 | 72.6 | 243 | 106.6 | 357 | 215 |
| M20 | EN 1665 | 116.9 | 487 | 166.5 | 694 | 434 |
FM is the assembly preload and MA the torque that produces it. The last column is an ISO 4014 hex bolt of class 8.8 under the same conditions: the flange bolt needs about 11 to 14 % more torque for the same preload. For serrated flanges use the supplier's torque or a torque–tension test.
Where Our Hex Flange Bolts Are Used
Automotive & trucks
Engines, gearboxes, axles, chassis brackets and body parts, mostly small series 10.9 with zinc flake.
Exhaust & manifolds
Flange bolts in stainless, A-286 and Inconel where heat would loosen a separate washer.
Agricultural & construction machinery
Serrated flange bolts on frames, guards and attachments that see constant vibration.
Solar & steel structures
Mounting rails, cable trays and light steel frames with slotted holes, where the flange bridges the slot.
HVAC, enclosures & sheet metal
Ducting, cabinets and panels, where the flange spreads load on thin sheet.
Pumps, valves & marine
A4, duplex and Monel flange bolts on pump casings, covers and deck fittings.
Hex Flange Bolt Testing & Certification
| Test | Method | Applied to |
|---|---|---|
| Chemical analysis / PMI | Mill certificate; XRF PMI | Every heat; 100 % of stainless and exotic alloy lots |
| Wedge tensile | ISO 898-1 / ASTM F606 | Every heat-treatment lot; checks head-to-shank soundness |
| Proof load | ISO 898-1 / ASTM F606 | 8.8, 10.9 and SAE grades |
| Hardness | Rockwell C, surface and core | Every lot |
| Flange geometry | dc, edge thickness c, bearing-face runout | Every lot |
| Serrations | Tooth form and count against the drawing | Serrated lots |
| Thread & dimensions | Thread gauges; across flats, head height, length | Every lot |
| Coating | Thickness; salt spray on request | Coated lots |
Every flange bolt lot ships with
- EN 10204 3.1 certificate with heat number
- Tensile or proof load and hardness results
- Dimensional and thread gauge record
- Heat treatment and coating record
- PMI report for stainless and exotic alloys
On request
- EN 10204 3.2 witnessed by TUV, DNV, Lloyd's, BV or SGS
- Torque–tension (friction) test report
- Salt spray test on coated bolts
- PPAP-style dimensional layout
Hex Flange Bolt Questions, Answered
A hex flange bolt is a hexagon head bolt with a round flange formed in one piece under the head. The flange acts as a built-in washer: it spreads the clamp load over a larger area, covers oversized or slotted holes and saves handling a separate washer. Metric flange bolts are made to EN 1665 (heavy series, formerly DIN 6921) and ISO 4162 or ISO 15071 (small series); inch hex flange screws are made to IFI-111 and ASME B18.2.1.
Heavy series bolts to EN 1665 cover M5 to M20 and use the same hexagon as an ISO 4014 hex bolt, for example 16 mm for M10 and 18 mm for M12. Small series bolts to ISO 4162 and ISO 15071 cover M5 to M16 with a smaller hexagon, 13 mm for M10 and 15 mm for M12, and a slightly smaller flange. Small series bolts save weight and space and are common in vehicles; heavy series bolts suit general engineering where standard spanners are used.
DIN 6921 was withdrawn and replaced by DIN EN 1665. The flange diameters are the same, but EN 1665 enlarged the hexagon from M10 to M20: 15 to 16 mm for M10, 16 to 18 mm for M12, 18 to 21 mm for M14, 21 to 24 mm for M16 and 27 to 30 mm for M20, and most heads became slightly taller. Old DIN 6921 bolts and EN 1665 bolts therefore need different spanners from M10 upward. We supply both; please state which one your drawing calls for.
Normally not. For every size from M5 to M20 the EN 1665 flange is larger than the outside diameter of an ISO 7089 plain washer, for example 26.6 mm against 24 mm for M12, and the ISO 4162 small series flange is also larger. Serrated flange bolts must never be used with a washer, because the serrations have to grip the joint surface itself.
Use serrated flange bolts where vibration could loosen the joint and slight marking of the surface is acceptable, for example on steel brackets, frames and machinery. The serrations bite into the clamped surface and resist rotation. Use plain flange bolts on painted, coated or soft surfaces, on surfaces harder than the bolt, and where the joint is often taken apart, because serrations damage coatings and lose effect on hard surfaces.
Calculated by the VDI 2230 method at 90 percent of minimum yield and a friction coefficient of 0.14, an EN 1665 M10 class 10.9 flange bolt needs about 83 N m for about 39 kN preload and an M12 about 145 N m for about 56 kN. This is roughly 11 to 14 percent more than a plain hex bolt of the same size and class, because the flange has a larger friction radius. These values do not apply to serrated flanges; use the manufacturer's figures or a torque-tension test for those.
EN 1665 and ISO 4162 list property classes 8.8 and 10.9 in steel and A2-70 in stainless steel. ISO 15071 adds class 9.8 and the fine pitch ISO 15072 also lists 12.9. Inch hex flange screws are made in SAE J429 Grade 5 and Grade 8, ASTM A449 and A354 BD, and ASTM F593 stainless. We also make flange bolts in A4 stainless, duplex, Inconel, Monel and titanium.
Inch hex flange screws are made to IFI-111, which ASME B18.2.1 also covers, in sizes 1/4 to 3/4 inch. A 1/2 inch screw has a 3/4 inch hexagon, a flange up to 1.07 inch across, a bearing circle of at least 0.98 inch and a head up to 0.51 inch high. The full table for 1/4 to 3/4 inch is given on this page.