--- title: "What Are Hex Nuts, Grade C Used For?" description: "Hex Nuts, Grade C (ISO 4034) are used for the clamped counter-face of a bolted joint. Catalogued M5 to M48. Typical industries, sizing and material selection." url: https://engineeringhardware.com/applications/hex-nuts-grade-c/ source: Engineering Hardware & Fasteners --- # What Are Hex Nuts, Grade C Used For? Nuts · ISO 4034 · Application guide Typical applications, the industries that specify hex nuts, grade c, and how to choose the right size, material and finish for the joint. Hex Nuts, Grade C are used for the clamped counter-face of a bolted joint. They are manufactured to ISO 4034, 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:** The clamped counter-face of a bolted joint - **Governing standard:** ISO 4034 - **Thread size range:** M5 to M48 - **Category:** Nuts Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation. ![What Are Hex Nuts, Grade C Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/06/Hex-Nuts-Grade-C-—-ISO-4034.webp) Hex Nuts, Grade C are used primarily for the clamped counter-face of a bolted joint. This page lists the industries and assemblies where they are specified, the selection criteria that matter for each application, installation practice, and the cases where a different fastener type is the correct choice. Parts are supplied to ISO 4034. Stocked across roughly M5 to M48, they cover general to heavy-duty work. ## Typical Applications for Hex Nuts, Grade C The most common settings where these are specified: - **Frames & weldments:** captive or welded options for repeatable assembly. - **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. - **Bolted joints:** the clamping counter-face on studs and bolts across every assembly type. ## How to Specify Hex Nuts, Grade C for Your Application - **Size:** Match the nominal size to the mating thread or hole. This product spans M5–M48; check the full table below for the exact dimensions of each size. - **Locking & grade:** Match the strength grade to the bolt, and choose a locking style (nyloc, all-metal, serrated flange) if the joint sees vibration. - **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 ISO 4034. Quoting the standard on your order guarantees interchangeable dimensions between suppliers. ## Installation & Assembly Practice - Run the nut down by hand before applying the wrench to catch cross-threading early. - Tighten the nut rather than the bolt head where access allows — the torque-to-preload relation is more consistent. - For locking styles, note that nyloc inserts are single-use in critical joints and lose grip above roughly 120 °C. ## Common Selection Mistakes with Hex Nuts, Grade C - Pairing a high-class bolt with a lower-class nut — the nut strips before the bolt reaches proof load; the nut class must meet or exceed the bolt class. - Using a plain nut with a spring washer in severe vibration instead of a prevailing-torque locking nut. - Re-using nyloc nuts in critical joints. ## Where Hex Nuts, Grade C Are Not the Right Choice Not on their own — they need a matching bolt or stud — and a plain nut is not a substitute for a locking type under heavy vibration. Custom manufacturing · Made to drawing ## Need a hex nuts, grade c outside the standard range? Thread, height, across-flats, property class, locking feature and flange form can all be varied, including thread sizes the standard series does not run to. Made by cold heading or tapping. Minimum order from 2,000 pieces; samples within 7 days of drawing approval. [Custom nut manufacturing](https://engineeringhardware.com/custom/nuts/)[Send a drawing](https://engineeringhardware.com/custom/nuts/#rfq) ## Technical Drawing Dimensioned line drawing of M5 Hex Nuts, Grade C to ISO 4034. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected. - **Pitch (mm):** 0.8 - **Width across flats s (mm):** 8.0 - **Width across corners e min (mm):** 8.63 - **Nut height m (mm):** 4.7 - **Product grade:** Grade C ## Dimensions & Specifications (ISO 4034) | Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Nut height m (mm) | Product grade | Reference standard | | --- | --- | --- | --- | --- | --- | --- | | M5 | 0.8 | 8.0 | 8.63 | 4.7 | Grade C | ISO 4034 / DIN 555 | | M6 | 1.0 | 10.0 | 10.89 | 5.2 | Grade C | ISO 4034 / DIN 555 | | M8 | 1.25 | 13.0 | 14.2 | 6.8 | Grade C | ISO 4034 / DIN 555 | | M10 | 1.5 | 16.0 | 17.59 | 8.4 | Grade C | ISO 4034 (DIN 555 specifies a smaller width across flats at this size) | | M12 | 1.75 | 18.0 | 19.85 | 10.8 | Grade C | ISO 4034 (DIN 555 specifies a smaller width across flats at this size) | | M14 | 2.0 | 21.0 | 22.78 | 12.8 | Grade C | ISO 4034 (DIN 555 specifies a smaller width across flats at this size) | | M16 | 2.0 | 24.0 | 26.75 | 14.8 | Grade C | ISO 4034 / DIN 555 | | M18 | 2.5 | 27.0 | 29.56 | 15.8 | Grade C | ISO 4034 / DIN 555 | | M20 | 2.5 | 30.0 | 33.53 | 18.0 | Grade C | ISO 4034 / DIN 555 | | M22 | 2.5 | 34.0 | 37.29 | 19.4 | Grade C | ISO 4034 (DIN 555 specifies a smaller width across flats at this size) | | M24 | 3.0 | 36.0 | 39.55 | 21.5 | Grade C | ISO 4034 / DIN 555 | | M27 | 3.0 | 41.0 | 45.2 | 23.8 | Grade C | ISO 4034 / DIN 555 | | M30 | 3.5 | 46.0 | 50.85 | 25.6 | Grade C | ISO 4034 / DIN 555 | | M36 | 4.0 | 55.0 | 60.79 | 31.0 | Grade C | ISO 4034 / DIN 555 | | M42 | 4.5 | 65.0 | 71.3 | 34.0 | Grade C | ISO 4034 / DIN 555 | | M48 | 5.0 | 75.0 | 82.6 | 38.0 | Grade C | ISO 4034 / DIN 555 | 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 ### Are Hex Nuts, Grade C made to a recognized standard? Yes — they are manufactured to ISO 4034, so dimensions are interchangeable between suppliers when you quote the standard on your order. ### What are Hex Nuts, Grade C used for? The clamped counter-face of a bolted joint. They are supplied to ISO 4034. ### Which industries use Hex Nuts, Grade C? They are commonly specified in frames & weldments, general machine building and maintenance & repair (mro), among other sectors. ### How do I choose the right size of Hex Nuts, Grade C? Match the nominal size to the mating thread or hole. This product is available from M5 to M48; the full dimension table on this page lists each size. ### Can I get a quote for Hex Nuts, Grade C 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: [Hex Nuts, Grade C — specifications & sizes](https://engineeringhardware.com/fastener/hex-nuts-grade-c/) ### Hex Nuts, Grade C Specification Guides ### Related Fastener Applications