MF Locknut | Concave Square Nut HDG | Poleline Hardware | Yokelink
The Yokelink MF Curved Locknut (also known as a Concave Locknut) is an essential secondary fastener designed to prevent primary nuts from loosening under severe vibration, wind loads, or thermal expansion on utility poles and transmission structures.
How It Works:
Unlike typical prevailing-torque locknuts, the MF locknut features a slightly curved (concave) square design. It spins freely onto the bolt threads by hand until it makes contact with the regular square nut. Once touching, applying an additional 1/2 to 3/4 turn with a wrench flattens the locknut. This deflection forces the locknut's threads to bite fiercely into the bolt's threads, creating a permanent, vibration-proof mechanical lock.
Manufactured from high-quality steel and fully Hot Dip Galvanized (HDG) to ASTM A153, these locknuts provide exceptional reliability and ease of installation for linemen.
Key Features of MF Curved Locknut
Design: Concave / Curved square shape for free-spinning installation.
Function: Locks securely against the primary nut to resist severe vibration.
Efficiency: Installs easily by hand; requires only a standard wrench to lock.
Corrosion Resistance: Hot Dip Galvanized for long-term outdoor durability.
Production Process of MF Curved Locknut
MF Curved Locknuts are manufactured from ASTM A307 carbon steel. The process starts with material preparation and cold forging to form the square body with a unique concave/curved locking profile. A central hole is punched, followed by precision tapping to create oversized internal threads. Heat treatment is applied to meet mechanical requirements. All nuts are hot‑dipped galvanized per ASTM A153 for corrosion resistance. Production and inspection comply with IEEE C135.1 and IEEE C135.80 standards.
Yokelink Quality Control and Testing Equipments
We don't just reference standards; we also verify them in practice: each batch of products undergoes destructive tensile testing in our internal laboratory to ensure load performance exceeds the minimum requirements of IEEE C135.1 / IEEE C138.80 or CSA specification; we use optical comparators to ensure the geometric accuracy of chamfered tips and rolled threads, enabling convenient on-site installation; at the same time, we conduct comprehensive testing on Rockwell hardness, coating thickness, and other parameters, and each shipment is accompanied by the original manufacturer's material specifications (MTRs) and quality inspection reports, with all data traceable back to the raw material furnace number.
The Application of MF Curved Locknut
MF Curved Locknuts are high‑security locking nuts widely used in overhead transmission and distribution lines, pole hardware, cross arms, and vibration‑prone connections. Their unique curved locking design delivers excellent anti‑loosening performance under long‑term vibration and outdoor loads. Made from ASTM A307 carbon steel and hot‑dip galvanized per ASTM A153, they provide strong corrosion resistance. Fully compliant with IEEE C135.1 and IEEE C135.80 standards, they ensure stable, safe, and maintenance‑free fastening for power line systems.
Yokelink Product Quality Inspection Report
We provide comprehensive inspection services for machine bolts, including SGS test bolts and formal Production Part Inspect Report (PPIR). The SGS tests verify the bolts’ compliance with international standards like ASTM A307 and IEEE C135.80, covering mechanical properties and corrosion resistance. The PPIR details all inspection items, ensuring each machine bolt meets dimensional, performance and quality requirements, providing reliable quality assurance for overhead line and industrial applications.
Technical Specifications of MF Curved Locknut
| Part No. |
Size |
Width |
Height |
Weight |
| Inch (B) |
Inch (A) |
Kg / Pcs |
| A1138 |
3/8"-16 |
5/8 |
1/4 |
0.008 |
| A1112 |
1/2"-13 |
13/16 |
19/64 |
0.011 |
| A1158 |
5/8"-11 |
1 |
3/8 |
0.017 |
| A1134 |
3/4"-10 |
1-1/8 |
7/16 |
0.025 |
| A1178 |
7/8"-9 |
1-5/16 |
15/32 |
0.032 |
| A1110 |
1"- 8 |
1-1/2 |
15/32 |
0.049 |
Cross Reference (Industry Equivalents):
| Size |
Part No. |
HUBBELL |
MACLEAN |
| 3/8"-16 |
A1138 |
3510 |
J8581 |
| 1/2"-13 |
A1112 |
3511 |
J8582 |
| 5/8"-11 |
A1158 |
3512 |
J8583 |
| 3/4"-10 |
A1134 |
3513 |
J8584 |
| 7/8"-9 |
A1178 |
3514 |
J8584-1/2 |
| 1"- 8 |
A1110 |
3515 |
|
(Note: Manufacturer part numbers are for reference only. Yokelink products are interchangeable based on IEEE standards.)
Frequently Asked Questions (FAQ)
Q1: What does "MF" stand for in an MF Locknut?
A: "MF" originally stood for MacLean-Fogg, the company that pioneered this style of fastener. Today, it is used as a standard industry term across poleline hardware to describe a curved or concave square locknut.
Q2: How do you properly install a concave MF locknut?
A: First, fully tighten your standard primary nut (such as a regular square or heavy hex nut) to secure the hardware. Then, thread the MF locknut onto the bolt. It will spin freely with your fingers. Once the MF locknut contacts the primary nut, use a wrench to tighten it an additional 1/2 to 3/4 turn. This flattens the concave shape, binding the threads and creating a secure lock against vibration.
Q3: Can an MF Locknut be used by itself without a primary nut?
A: No. An MF locknut is a secondary "jam nut" designed specifically to lock against a primary nut. It does not have the thickness or load-bearing capacity to secure poleline crossarms or hardware on its own.
Value-Added Supply Chain Services
1. Blanket Order & Free Warehousing
Yokelink offers Blanket Order programs: Place an annual order to lock prices, we manufacture your total volume and hold stock in our facility free of charge. Split Shipments: Schedule partial shipments (e.g., monthly or quarterly) based on your project progress. You get the benefits of just-in-time delivery without the risk of shortages.
2. DDP Shipping (USA Duties Included)Landed Cost Certainty
We handle the complex logistics. Our DDP (Delivered Duty Paid) service covers sea freight, US Customs clearance, and Section 301 tariffs. The price we quote is the final price delivered to your door / Warehouse.
3. Free Sample Program
We offer Free Samples to qualified commercial buyers for testing and approval.
Reference Information:
For IEEE C135.1 technical details behind our specification, see Understanding IEEE C135.1 Standard
IEEE C135.1 Specification Download:
How to Choose the Right Machine Bolt Under IEEE C135.1
