Flange bolt (hex flange bolt)

01

Fix the standard, size and thread length

CDE Fasteners' DIN 6921 datasheet describes a one-piece hex washer-head bolt with a flat bearing surface; it says the flange removes the need for a flat washer, helps compensate for a misaligned hole, and with a matching flange nut resists slippage by spreading clamp load, and that 10.9 flange bolts are used mainly on truck chassis frames. It tabulates M5 to M12: for example M8 with 13 mm across flats and an 18 mm maximum flange, M10 with 15 mm and 22.3 mm, and M12 with 16 mm and 28.6 mm; thread lengths of 22, 26 and 30 mm for M8, M10 and M12 bolts up to 125 mm long; and length tolerances from ±0.35 mm (12–16 mm) to ±0.8 mm (130–180 mm). [1]

Haiyan Bolt, a linked supplier, lists hex flange bolts to DIN 6921 and ASME B18.2.1 from 6 to 30 mm and 1/4 to 1 in, in grades 4.8 to 12.9 and Gr 2 to Gr 10, and A2 (304) and A4 (316) stainless, and notes that some flange bolts have locking serrations under the flange. [2]

Editorial calculation: the M10 bolt's 22.3 mm maximum flange is about 22.3 / 15 ≈ 1.49 times its width across flats; check that the flange fits next to walls, radii or other fasteners in your joint.

Give the supplier the standard (DIN 6921, ASME B18.2.1 or drawing), thread size, pitch and length, thread length, plain or serrated flange, property class or grade, material, finish and coating thickness, matching nut, quantity, packing, and certificates (material, mechanical tests, coating).

02

Set the property class and finish

CDE gives Class 8.8 carbon steel bolts minimum tensile strength of 800 N/mm², proof stress of 640 N/mm² and hardness Rockwell C22–32; Class 10.9 alloy steel bolts 1,040 N/mm² tensile, 940 N/mm² proof and HRC 32–39, both tempered at 425 °C minimum; and A2-70 stainless bolts 700 N/mm² tensile, for low-strength uses where corrosion resistance matters. Finishes include black phosphate, zinc and plain. [1]

Haiyan lists finishes of zinc plating, plain, black oxide, hot-dip galvanising, mechanical galvanising and Dacromet. [2]

Editorial calculation: Class 10.9's 940 N/mm² proof stress is about 940 / 640 ≈ 1.47 times Class 8.8's. Pair the bolt with a nut of matching class and confirm proof load on the certificate.

NASA's Fastener Design Manual (Reference Publication 1228, 1990) adds the installation side. It relates tightening torque to preload as T = K·D·P and warns against using K = 0.2 without thought, suggesting 0.15 as a more realistic value for steel on steel; its table of torque coefficients gives K from 0.074 to 0.250 as friction coefficients rise from 0.05 to 0.20. Quoting the Industrial Fasteners Institute, it rates preload accuracy at ±35% by feel, ±25% with a torque wrench, ±15% by turn of the nut, ±10% with load-indicating washers, ±3–5% by fastener elongation and ±1% with strain gauges, at relative costs of 1, 1.5, 3, 7, 15 and 20. On serrated faces it notes that the serrations dig into the bearing surface during final tightening, so they cannot be used with a washer or on surfaces where scratches or corrosion would be a problem, and it reports SPS Technologies' finding that its serrated-face bolts needed 110% of tightening torque to loosen. [3]

Editorial calculation: for an M10 bolt and a target preload of 20 kN, T = K·D·P gives 0.15 × 0.010 m × 20,000 N = 30 N·m at K = 0.15 but 40 N·m at K = 0.2; tightened to 30 N·m with K actually at 0.2, the preload would be 15 kN, 25% short. State the lubricant or coating with the torque value. [3]

TR Fastenings' table of ISO 898-1 mechanical properties separates two figures that are easy to confuse. For class 8.8 up to 16 mm it lists minimum tensile strength of 800 MPa, minimum 0.2% proof strength (Rp0.2) of 640 MPa and a test (proof-load) stress of 580 MPa, rising above 16 mm to 830, 660 and 600 MPa; class 10.9 gives 1,040, 940 and 830 MPa and class 12.9 1,220, 1,100 and 970 MPa, with minimum elongation of 12%, 9% and 8%. Its ISO 898-7 table of minimum breaking torque for an M10 × 1.5 thread lists 66 N·m for 8.8, 81 N·m for 10.9 and 90 N·m for 12.9. [4] Editorial calculation: the 30–40 N·m tightening torque worked out above for an M10 at 20 kN is 45–61% of the 66 N·m minimum breaking torque of class 8.8; when a certificate quotes 640 MPa for 8.8, check whether it is the 0.2% proof strength or the 580 MPa proof-load stress used in the bolt proof test. [4] [3] [1]

03

Compare what suppliers offer

Suppliers linked to this page list hex flange bolts; each card links to the page reviewed.

Listings include DIN 6921 and ASME hex flange bolts in carbon, alloy and stainless steel, and flange bolts alongside nuts, washers and screws from fastener makers. Sites that could not be reached are hidden here. Ask each for standard, class, finish, certificates and minimum order.

04

Trace the bolt features

This is a functional reference built from the sources cited; it is not one maker's specification.

05

Fill the specification fields with values for your joint

A flange bolt quotation needs values for your joint. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the standard, size and class data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Standard: [DIN 6921; ASME B18.2.1]
Size: [thread; pitch; length; thread length]
Flange: [plain; serrated]
Class: [8.8; 10.9; A2-70; SAE grade]
Finish: [type; thickness]
Nut: [matching class]
Quantity: [lot; packing]
Certificates: [material; mechanical; coating]

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