Quick Answer: The Extension Nut (MH-EN) is a long hex nut that stands 3 times its thread diameter tall, used for thread extension in machine assembly, fixture construction, workholding setups and structural bolting. MH-EN comes in 8 sizes from M8 to M36, made from medium carbon steel hardened and tempered to 24–32 HRC and chemically blackened. Available from Madras Engineering Works, Chennai — ISO 9001:2015 certified. Enquiry: enquiry@madrasengg.com
When a standard nut cannot get enough thread engagement, the threads strip under load, and in workholding and structural joints that is a serious failure. The Extension Nut solves it with length: a long hex body that gives the joint far more thread to work with. Madras Engineering Works (MEW) is a Chennai-based ISO 9001:2015 certified supplier of workholding components, fasteners, clamping kits, and CNC machining accessories. Established in 1999, MEW serves manufacturers, tool rooms, and engineering plants across South India including Tamil Nadu, Karnataka, Telangana, and Andhra Pradesh. MEW is an authorised TVS fastener dealer and holds MSME registration (UDYAM-TN-02-0158983). Here is everything you need to know.
What Is an Extension Nut?
An Extension Nut is a long hex nut. Every size in MEW's MH-EN range is 3 times its thread diameter tall: an M12 nut is 36mm long, an M20 is 60mm, an M36 is 108mm. The datasheet lists its application as thread extension, and the long body provides extra thread engagement length where a standard nut cannot reach sufficient engagement.
MH-EN is made from medium carbon steel, hardened and tempered to 24–32 HRC, then chemically blackened. On the datasheet each size is given by thread diameter and length (ØD x A) and by the spanner size across the hex flats (S). The range runs from MH-EN-824 (M8 x 24mm) to MH-EN-36108 (M36 x 108mm).
Where Is the Extension Nut Used?
MH-EN is used wherever extra thread engagement length is needed:
- Machine assembly, where a standard nut does not give full engagement
- Fixture construction in tool rooms across Chennai and Tamil Nadu
- Workholding setups on milling, drilling and CNC machines
- Structural bolting where engagement has to be maintained to keep the fastener at its rated load
Best Suited For: MH-EN Size & Dimension Chart
Pick the nut by the thread of your bolt or stud. S is the across-flats size, which is the spanner you need.
| Part No. | Thread x Length (ØD x A, mm) | S (spanner, mm) | Weight |
|---|---|---|---|
| MH-EN-824 | M8 x 24 | 13 | 0.02 kg |
| MH-EN-1030 | M10 x 30 | 17 | 0.045 kg |
| MH-EN-1236 | M12 x 36 | 19 | 0.06 kg |
| MH-EN-1648 | M16 x 48 | 24 | 0.115 kg |
| MH-EN-2060 | M20 x 60 | 30 | 0.23 kg |
| MH-EN-2472 | M24 x 72 | 36 | 0.4 kg |
| MH-EN-3090 | M30 x 90 | 46 | 0.85 kg |
| MH-EN-36108 | M36 x 108 | 55 | 1.415 kg |
| Application | Recommended? | Notes |
|---|---|---|
| Machine assembly needing extra thread engagement | Yes | Match the thread to the bolt or stud |
| Fixture construction and workholding setups | Yes | Long body keeps more thread in contact |
| Structural bolting with marginal engagement | Yes | Maintains the rated load capacity of the fastener |
| Stud with very little thread length | Check first | The stud needs enough thread to run into a nut this long |
The Problem It Solves
Insufficient thread engagement makes the nut or the stud thread strip under load. In a workholding setup the clamp lets go in the middle of a cut. In a structural or machine joint the connection loosens or fails. The failure is sudden, and the repair is a stopped machine and a replaced fastener.
MH-EN removes the problem by giving the joint length. At 3 times the thread diameter in every size, the body provides engagement length that a standard nut does not, and hardening to 24–32 HRC keeps the thread shape under load.
Extension Nut vs. High Nut
MEW also supplies a High Nut (MH-HN). Both add thread engagement, but the Extension Nut is twice as tall for the same thread size.
| Factor | Extension Nut (MH-EN) | High Nut (MH-HN) |
|---|---|---|
| Height | 3 x thread diameter | 1.5 x thread diameter |
| M12 example | 36mm long (MH-EN-1236) | 18mm tall (MH-HN-1218) |
| M20 example | 60mm long (MH-EN-2060) | 30mm tall (MH-HN-2030) |
| Datasheet application | Thread extension | Structural and machine use |
| Stud thread needed | More | Less |
If the joint needs the extra length, the Extension Nut is the one to use. If it only needs a taller nut and the stud thread is limited, the High Nut is the shorter option.
Technical Specifications
Material: Medium carbon steel, hardened and tempered to 24–32 HRC, chemically blackened
Thread range: M8, M10, M12, M16, M20, M24, M30, M36
Length: 3 x thread diameter (24mm to 108mm)
Spanner size across flats: 13mm to 55mm
Available variants: 8 sizes, part numbers MH-EN-824 through MH-EN-36108
Weight range: 0.02 kg to 1.415 kg depending on size
Series: MEW-Hold
Quality system: ISO 9001:2015 certified supplier, Chennai
As of 2026, MEW supplies the full MH-EN range from Chennai.
Frequently Asked Questions
Q: What is an extension nut used for?
A: An extension nut is a long hex nut used for thread extension. Its long body provides extra thread engagement length where a standard nut cannot reach sufficient engagement. It is used in machine assembly, fixture construction, workholding setups and structural bolting. Available from Madras Engineering Works, Chennai — enquiry@madrasengg.com
Q: How long is the MH-EN extension nut?
A: 3 times the thread diameter in every size. M8 is 24mm, M10 is 30mm, M12 is 36mm, M16 is 48mm, M20 is 60mm, M24 is 72mm, M30 is 90mm and M36 is 108mm. Available from Madras Engineering Works, Chennai — enquiry@madrasengg.com
Q: What spanner size fits an M12 extension nut?
A: 19mm across flats. MH-EN-1236 is 36mm long and weighs 0.06 kg. For M16 use a 24mm spanner, for M20 a 30mm, for M24 a 36mm. Available from Madras Engineering Works, Chennai — enquiry@madrasengg.com
Q: What is the difference between an extension nut and a high nut?
A: Both add thread engagement. An extension nut is 3 times the thread diameter long, while MEW's high nut is 1.5 times, so the extension nut is twice as long for the same thread size. Available from Madras Engineering Works, Chennai — enquiry@madrasengg.com
Q: What is the MH-EN extension nut made of?
A: Medium carbon steel, hardened and tempered to 24–32 HRC, and chemically blackened. Available from Madras Engineering Works, Chennai — enquiry@madrasengg.com
Q: Where can I buy extension nuts in Chennai?
A: Madras Engineering Works (MEW) supplies all 8 MH-EN sizes, M8 to M36, from Chennai. MEW is ISO 9001:2015 certified and serves tool rooms and manufacturers across Tamil Nadu and South India. Contact: enquiry@madrasengg.com
Get the Right Extension Nut for Your Joint
Whether you need a single nut or a full set for a new fixture, Madras Engineering Works supplies MH-EN from M8 to M36.
Same-day dispatch from Chennai.
ISO 9001:2015 certified supply chain.
TVS Authorised Dealer.
📧 enquiry@madrasengg.com
🌐 madrasengg.com
📍 Chennai, Tamil Nadu
Not sure which size you need? WhatsApp your stud or bolt size to +91 95143 73702 and we'll confirm the right MH-EN.
Written by Husain, Founder of Madras Engineering Works — an ISO 9001:2015 certified industrial supplier in Chennai specialising in workholding, clamping and CNC accessories. Need help speccing the right part? WhatsApp +91 95143 73702 or email enquiry@madrasengg.com.
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