ASME B18.2.3.9M Heavy Hex Flange Screws (Metric)
Metric heavy hex flange screws per ASME B18.2.3.9M — dimension table for M10 to M20: body diameter, heavy-series width across flats/corners, flange diameter Dc, bearing circle Dw, flange edge thickness C, head height K, wrenching height K1, fillet radius R.
Last updated: 2026-11
Specifications
B18.2.3.9M is where the flanged head meets the heavy hex series: the same integrated bearing flange as B18.2.3.4M, but on the enlarged heavy-hex head dimensioned for high preload. The collected table covers M10 - M20, and the heavy-series signature is visible in the across-flats column — the table prints 15/14.57 at M10, 18 at M12, 24 at M16 and 30 at M20, every size above the standard-series flange ladder (13 at M10, 15 at M12, 21 at M16 in the B18.2.3.4M table). The flange grows with it: Dc max 22.3 mm at M10, 26.6 at M12, 43 at M20, with bearing circle Dw min (19.6 at M10, 39.9 at M20) and flange edge thickness C min (1.5 at M10 to 3 at M20) proportioned for the higher clamp loads. The page's own footnote defines the manufacturing constraint that makes this series distinct: the reduced body diameter Dsi is the blank diameter before thread rolling, and a shoulder is mandatory when the body is reduced — relevant when your RFQ involves rolled-thread production rather than cut threads. Head height K (8.6 max at M10 to 17.7 at M20), wrenching height K1 and fillet radius R complete the geometry. Strength classes are not tabulated — per RFQ.
| Standard | ASME B18.2.3.9M — metric heavy hex flange screws, coarse pitch, sizes M10 - M20 (M10 x 1.5, M12 x 1.75, M14 x 2, M16 x 2, M20 x 2.5) |
|---|---|
| Width across flats S | Heavy-series ladder (M10: 15/14.57; M12: 18/17.57; M14: 21/20.48; M16: 24/23.48; M20: 30/29.16 as tabulated) — every size above the standard-series flange ladder of the same M-size |
| Flange geometry | Flange diameter Dc max (M10: 22.3; M12: 26.6; M20: 43), bearing circle Dw min, flange edge thickness C min (M10: 1.5 rising to 3 at M20) — heavy-preload bearing on the integrated flange |
| Head height K | Max/min (M10: 8.6/-; M12: 10.4/-; M20: as tabulated), wrenching height K1 min (M10: 3.7; M12: 4.6) |
| Body diameter Ds | Max = nominal, min for rolling (M10: 9.78; M12: 11.73; M20: 19.67); footnote: reduced body Dsi is the pre-rolling blank and a shoulder is mandatory when reduced |
| Fillet radius R | Max per size (0.6 at M10 rising through the ladder) — header prints "Fille Radius" on the source, carried verbatim |
| Not tabulated | Strength classes, proof loads, thread lengths, finish — per RFQ |
| Nominal Dia., D, and Thread Pitch | Body Dia., D s | Body Dia., D s | Width Across Flats, S | Width Across Flats, S | Width Across Corners, E | Width Across Corners, E | Flange Dia., D c | Bearing Circle Dia., D w | Flange Edge Thickness, C | Head Height, K | Wrenching Height K1 | Fille Radius, R |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Nominal Dia., D, and Thread Pitch | Max | Min | Max | Min | Max | Min | Max | Min | Min | Max | Min | Max |
| ANSI B18.2.3.9M - M10 × 1.5 | 10 | 9.78 | 15 | 14.57 | 17.32 | 16.32 | 22.3 | 19.6 | 1.5 | 8.6 | 3.7 | 0.6 |
| ANSI B18.2.3.9M - M12 × 1.75 | 12 | 11.73 | 18 | 17.57 | 20.78 | 19.68 | 26.6 | 23.8 | 1.8 | 10.4 | 4.6 | 0.7 |
| ANSI B18.2.3.9M - M14 × 2 | 14 | 13.73 | 21 | 20.48 | 24.25 | 22.94 | 30.5 | 27.6 | 2.1 | 12.4 | 5.5 | 0.9 |
| ANSI B18.2.3.9M - M16 × 2 | 16 | 15.73 | 24 | 23.16 | 27.71 | 25.94 | 35 | 31.9 | 2.4 | 14.1 | 6.2 | 1 |
| ANSI B18.2.3.9M - M20 × 2.5 | 20 | 19.67 | 30 | 29.16 | 34.64 | 32.66 | 43 | 39.9 | 3 | 17.7 | 7.9 | 1.2 |
| All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. | All dimensions are in millimeters. Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced. |
- Header prints 'Fille Radius' (source spelling) and the trailing row repeats the reduced-body note in every column, carried verbatim.
Materials
- Heavy hex flange screws in this series are selected for high-preload joints and ship in carbon steel by property class (10.9 and up is the common pairing) and stainless A2/A4 where corrosion sets the material. The heavy-series head exists to survive high torque — state the property class and tightening method on the RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASME B18.2.3.9M Heavy Hex Flange Screws (Metric)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 1,000–10,000 pieces depending on size. Stock items run 3–7 days. High-strength and custom parts run 15–25 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
B18.2.3.4M or B18.2.3.9M — both are metric flange screws, so which one?
The head series decides it. The collected tables show the fork directly at M12: the standard-series flange screw (B18.2.3.4M) presents 15 mm across flats, the heavy-series (B18.2.3.9M) 18 mm, with a proportionally larger flange and deeper head. with a proportionally larger flange (26.6 vs 25 mm Dc max) and deeper head. The heavy series is the choice where the screw is tightened to high preload — the bigger hex resists the torque and the larger flange carries the bearing pressure. The practical buying rule: match the designation on the drawing, and check your socket stock — a 15 mm socket will not turn an 18 mm head, and a mixed delivery of the two series at the same M-size is a real assembly-line stopper.
What is the mandatory-shoulder note in the table footnote about?
The collected page's trailing note reads: "Reduced body diameter, Dsi, is the blank diameter before rolling. Shoulder is mandatory when body diameter is reduced." In production terms, a rolled-thread screw made on a reduced blank has a plain body thinner than the nominal thread diameter; where the application needs that body to locate or shear (a fitted body), the screw must carry a shoulder — an unthreaded cylindrical land at full nominal diameter — to do the job the reduced body no longer can. If your drawing calls a shoulder under the head, say so explicitly on the RFQ: it changes the manufacturing route and the price, and it is not visible in the head-geometry table.
Related knowledge
- What Bolt Property Classes 8.8, 10.9 and 12.9 Encode — and When High Strength Stops Being the Right Choice
- Bolt Grade Selection: ISO 898-1 8.8/10.9/12.9 vs ASTM A307 and A325
- 8.8 vs 10.9 vs 12.9 Bolts: Strength, Hardness and Cost — What the Evidence Settles
- Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
- How to Determine Tightening Torque and Choose a Tightening Method for a Bolted Joint
- Fastener Failure Modes: Which Fatigue, Creep and SCC Controls the Evidence Supports
- Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support