--- title: "What Are 12-Point Flange Screws Used For?" description: "12-Point Flange Screws (ASME B18.2.3.11M) are used for high-preload joints in confined recesses, where twelve engagement points let a socket enter at half th…" url: https://engineeringhardware.com/applications/twelve-point-flange-screws/ source: Engineering Hardware & Fasteners --- # What Are 12-Point Flange Screws Used For? Bolts · ASME B18.2.3.11M · Application guide Typical applications, the industries that specify 12-point flange screws, and how to choose the right size, material and finish for the joint. 12-Point Flange Screws are used for high-preload joints in confined recesses, where twelve engagement points let a socket enter at half the angular increment a hexagon allows. They are manufactured to ASME B18.2.3.11M, and the choice of size, property class and finish is driven by the load in the joint and the environment it sits in. - **Primary duty:** High-preload joints in confined recesses, where twelve engagement points let a socket enter at half the angular increment a hexagon allows - **Governing standard:** ASME B18.2.3.11M - **Thread size range:** M6 to M20 - **Category:** Bolts Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation. ![What Are 12-Point Flange Screws Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/09/12-Point-Screws-Bolts-Applications.webp) 12-Point Flange Screws (ASME B18.2.3.11M) are specified where the joint requires high-preload joints in confined recesses, where twelve engagement points let a socket enter at half the angular increment a hexagon allows. The sections below cover the typical end-uses by industry, the size and material decisions for each, assembly practice, and the applications this fastener type is not suited to. Stocked across roughly M6 to M20, they cover general to heavy-duty work. ## Typical Applications for 12-Point Flange Screws The most common settings where these are specified: - **Heavy machinery:** securing gearboxes, frames and guarding on plant that sees shock loads. - **Energy & infrastructure:** tower, pylon and pipework supports exposed to weather and long service life. - **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment. - **Maintenance & repair (MRO):** a stocked size for servicing existing plant where the original fastener spec must be matched. - **Fabrication & metalwork:** bench and on-site assembly of steel frames, enclosures and weldments. 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This product spans M6–M20; check the full table below for the exact dimensions of each size. - **Strength class:** Choose the property class (e.g. 8.8, 10.9, 12.9 or A2/A4 stainless) for the load and environment, and tighten to the matching torque so the joint relies on preload, not friction. - **Environment:** For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient. - **Standard:** This product is supplied to ASME B18.2.3.11M. Quoting the standard on your order guarantees interchangeable dimensions between suppliers. ## Installation & Assembly Practice - Tighten to the torque for the size and property class with a calibrated wrench — the joint is held by preload, not by the thread friction alone. - Ensure at least one full thread projects beyond the nut after tightening, and never re-use a bolt that has been tightened into yield. - Under slotted or oversized holes, fit a hardened washer so the preload does not relax into the hole edge. ## Common Selection Mistakes with 12-Point Flange Screws - Specifying class 12.9 "to be safe" in a corrosive environment — high classes are more sensitive to hydrogen embrittlement and stress corrosion; 8.8 hot-dip galvanized often outlasts them outdoors. - Choosing a length that puts the shear plane through the threaded portion when a plain shank (partially threaded bolt) was available. - Mixing stainless bolts with plated-steel nuts: the joint loses its corrosion logic and can gall or seize. ## Where 12-Point Flange Screws Are Not the Right Choice Not for permanent joints that will never be opened (a rivet or weld is cheaper), and not where the head must sit flush — use a countersunk screw instead. Custom manufacturing · Made to drawing ## Need a point flange screws outside the standard range? Head form and drive can be specified to the assembly rather than to a standard: a larger bearing face, a security drive, or a socket sized for the tool already on the bench. Made by cold heading or hot forging. Minimum order from 2,000 pieces; samples within 7 days of drawing approval. [Custom bolt manufacturing](https://engineeringhardware.com/custom/bolts/)[Send a drawing](https://engineeringhardware.com/custom/bolts/#rfq) ## Technical Drawing Dimensioned line drawing of M6 12-Point Flange Screws to ASME B18.2.3.11M. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected. - **Pitch (mm):** 1.0 - **Wrenching size across corners (mm):** 9.0 - **Flange diameter dc (mm):** 13.0 - **Head height k (mm):** 5.4 - **Common length range (mm):** 16~60 - **Property class:** 10.9 / 12.9 ## Dimensions & Specifications (ASME B18.2.3.11M) | Thread size | Pitch (mm) | Wrenching size across corners (mm) | Flange diameter dc (mm) | Head height k (mm) | Common length range (mm) | Property class | Reference standard | | --- | --- | --- | --- | --- | --- | --- | --- | | M6 | 1.0 | 9.0 | 13.0 | 5.4 | 16~60 | 10.9 / 12.9 | ASME B18.2.3.11M | | M8 | 1.25 | 11.0 | 16.6 | 7.2 | 20~80 | 10.9 / 12.9 | ASME B18.2.3.11M | | M10 | 1.5 | 13.0 | 20.5 | 9.0 | 25~100 | 10.9 / 12.9 | ASME B18.2.3.11M | | M12 | 1.75 | 16.0 | 24.4 | 10.8 | 30~120 | 10.9 / 12.9 | ASME B18.2.3.11M | | M14 | 2.0 | 18.0 | 28.0 | 12.6 | 35~140 | 10.9 / 12.9 | ASME B18.2.3.11M | | M16 | 2.0 | 21.0 | 32.2 | 14.4 | 40~160 | 10.9 / 12.9 | ASME B18.2.3.11M | | M20 | 2.5 | 27.0 | 40.0 | 18.0 | 50~200 | 10.9 / 12.9 | ASME B18.2.3.11M | Inside the plant ## Manufactured in our own plant This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided. 1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift. 2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g. 3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1. 4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227. ## Frequently Asked Questions ### What material should 12-Point Flange Screws be for outdoor use? For damp, coastal or chemical environments specify A4 (316) stainless or a suitably coated steel. For indoor or dry use, A2 (304) stainless or zinc-plated steel is normally adequate. ### Are 12-Point Flange Screws made to a recognized standard? Yes — they are manufactured to ASME B18.2.3.11M, so dimensions are interchangeable between suppliers when you quote the standard on your order. ### What are 12-Point Flange Screws used for? High-preload joints in confined recesses, where twelve engagement points let a socket enter at half the angular increment a hexagon allows. They are supplied to ASME B18.2.3.11M. ### Which industries use 12-Point Flange Screws? They are commonly specified in fabrication & metalwork, structural steel and automotive & transport, among other sectors. ### Can I get a quote for 12-Point Flange Screws in the size and material I need? Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time. ## Related Pages Product page: [12-Point Flange Screws — specifications & sizes](https://engineeringhardware.com/fastener/twelve-point-flange-screws/) ### 12-Point Flange Screws Specification Guides ### Related Fastener Applications