Technically reviewed by Vincent, Founder at HEXVARO
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DIN 6921 flange bolt dimensions (mm)
Flange diameter dc and head height k are maximum values. Width across flats s is the wrench size. Flange thickness c is the minimum thickness at the outer edge. Values are from the published DIN 6921 table.
| Size | Pitch P | Flange dia. dc max | Wrench size s | Head height k max | Flange thickness c min | Across corners e min | Inquiry |
|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 11.8 | 8 | 5.4 | 1.0 | 8.71 | Quote this size |
| M6 | 1.0 | 14.2 | 10 | 6.6 | 1.1 | 10.95 | Quote this size |
| M8 | 1.25 | 18.0 | 13 | 8.1 | 1.2 | 14.26 | Quote this size |
| M10 | 1.5 | 22.3 | 15 | 9.2 | 1.5 | 16.50 | Quote this size |
| M12 | 1.75 | 26.6 | 16 | 11.5 | 1.8 | 17.62 | Quote this size |
| M14 | 2.0 | 30.5 | 18 | 12.8 | 2.1 | 19.86 | Quote this size |
| M16 | 2.0 | 35.0 | 21 | 14.4 | 2.4 | 23.15 | Quote this size |
| M20 | 2.5 | 43.0 | 27 | 17.1 | 3.0 | 29.87 | Quote this size |
Wrench size: flange bolt vs standard hex bolt
The flange carries the bearing load, so the hex can be smaller than on a DIN 933 bolt. That saves weight and space, but it means you need different sockets on the assembly line. From M10 upwards the difference is one or more spanner sizes.
| Size | DIN 6921 flange bolt s | DIN 933 hex bolt s | ISO 4017 hex bolt s | Inquiry |
|---|---|---|---|---|
| M6 | 10 | 10 | 10 | Quote this size |
| M8 | 13 | 13 | 13 | Quote this size |
| M10 | 15 | 17 | 16 | Quote this size |
| M12 | 16 | 19 | 18 | Quote this size |
| M14 | 18 | 22 | 21 | Quote this size |
| M16 | 21 | 24 | 24 | Quote this size |
| M20 | 27 | 30 | 30 | Quote this size |
Thread length b (mm)
Partly threaded flange bolts use the usual reference thread length: 2d + 6 up to 125 mm length, 2d + 12 from 125 to 200 mm, and 2d + 25 above 200 mm. Short bolts are threaded up to the flange.
| Size | b for L ≤ 125 | b for 125 < L ≤ 200 | b for L > 200 | Inquiry |
|---|---|---|---|---|
| M6 | 18 | — | — | Quote this size |
| M8 | 22 | 28 | — | Quote this size |
| M10 | 26 | 32 | — | Quote this size |
| M12 | 30 | 36 | — | Quote this size |
| M16 | 38 | 44 | 57 | Quote this size |
| M20 | 46 | 52 | 65 | Quote this size |
Approximate weight per 1000 pcs (kg)
Weights are for plain steel (density 7.85 kg/dm³), from the published DIN 6921 mass table. The flange adds noticeable weight compared with a plain hex bolt plus no washer, so use these figures, not hex bolt weights, for freight planning.
| Size × length | kg / 1000 | Size × length | kg / 1000 | Inquiry |
|---|---|---|---|---|
| M6 × 16 | 7.62 | M6 × 30 | 10.5 | Quote this size |
| M8 × 20 | 16.25 | M8 × 40 | 23.68 | Quote this size |
| M10 × 25 | 30.42 | M10 × 50 | 45.21 | Quote this size |
| M12 × 30 | 51.46 | M12 × 60 | 77.21 | Quote this size |
| M14 × 40 | 81.58 | M14 × 80 | 129.81 | Quote this size |
| M16 × 40 | 103.47 | M16 × 80 | 166 | Quote this size |
Need these DIN 6921 / ISO 4162 sizes? Request a quote
- Published lengths run from about 10 mm (M5) up to 150 mm (M14, M16).
- For mixed orders, multiply quantity by weight per piece for each line and add packaging weight.
Plain vs serrated flange
DIN 6921 covers both a plain flange and a serrated (knurled) underhead. Serrations bite into the mating surface and resist rotation under vibration, which is why serrated flange bolts are common on vehicle chassis, machinery frames and steel framing.
Serrations damage paint and soft materials, and the marks can become corrosion sites. Use a plain flange on painted, coated or aluminium parts unless the drawing calls for serrations. Serrated flanges should not be used with a separate washer.
DIN 6921, EN 1665 and ISO 4162
DIN 6921 (heavy series) is withdrawn and replaced by DIN EN 1665. ISO 4162 is a different standard for small-series flange bolts: it covers M5 to M16, product grade A, property classes 8.8 to 10.9 and stainless A2-70. Small-series heads are more compact than the heavy series.
Because the head sizes differ, do not treat DIN 6921, EN 1665 and ISO 4162 as interchangeable without checking wrench size, flange diameter and head height against your drawing.
Grades and finishes
- Property class 8.8 is the most common; 10.9 is used for higher-load joints.
- Stainless A2-70 is covered by ISO 4162 (small series).
- Zinc plated (bake 10.9 after plating), zinc flake for 10.9 and coastal or vehicle use, or plain.
- If hot-dip galvanizing is required, order matching oversize-tapped flange nuts and check that serrations are acceptable after coating.
How to specify flange bolts in your RFQ
- Standard and edition: DIN 6921, EN 1665 or ISO 4162, and the wrench size you need.
- Plain or serrated flange.
- Size × length and full or partial thread.
- Property class 8.8 or 10.9 (or A2-70) and finish with a full designation.
- Matching flange nut (e.g. DIN 6923) if required, quantity per size and packaging.
Order these sizes from HEXVARO
Send your size list with grade, finish and quantity — we reply within 2 working hours with price, lead time and shipping terms.
- Reply: within 2 working hours
- MOQ: 500 pcs per specification
- Lead time: 10–15 days stock items
- Payment: T/T · L/C · PayPal
- Shipping ports: Tianjin · Ningbo · Shanghai · Shenzhen
- Incoterms: EXW · FOB · CFR · CIF · DAP
- Experience: Founder with 10+ years in the fastener industry
Frequently asked questions
What wrench size is an M10 flange bolt?
15 mm for DIN 6921. A DIN 933 hex bolt of the same size takes 17 mm, and an ISO 4017 bolt takes 16 mm.
What wrench size is an M12 flange bolt?
16 mm for DIN 6921, compared with 19 mm for DIN 933 and 18 mm for ISO 4017.
What is the difference between serrated and plain flange bolts?
Serrations under the flange bite into the surface to resist loosening from vibration. Avoid them on painted or soft surfaces you do not want marked.
Is DIN 6921 the same as ISO 4162?
Not exactly. DIN 6921 has been replaced by EN 1665 (heavy series). ISO 4162 is a small-series flange bolt with more compact heads. State the standard and wrench size you need.
Do flange bolts need a separate washer?
Usually not. The integrated flange spreads the load. On slotted or soft materials a hardened washer may still be specified, but not under a serrated flange.
What is the MOQ for flange bolts?
Reference MOQ is 500 pcs per specification. Stock sizes typically ship in 10–15 days and made-to-order sizes in 25–30 days, subject to quotation. We reply to every RFQ within 2 working hours.
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