MJ Thread Auto-Lok Nuts for Aerospace Applications

What is an MJ thread?

MJ is the aerospace metric thread form. It is similar in purpose to UNJ, but MJ is measured in metric units while UNJ is measured in imperial units. Both thread forms are used where fatigue performance and controlled tolerances are important.

The MJ thread standard is specified in ISO 5855-2. Compared with general metric threads, the MJ form uses a larger root radius, a larger minor diameter and stricter pitch diameter tolerance. These features help support better fatigue behavior in aerospace joints, especially in high-vibration and high-load assemblies such as engines, actuators, brackets and flight-critical hardware.

Why choose Auto-Lok MJ self-locking nuts?

Auto-Lok MJ nuts are designed for aerospace assemblies where conventional metric lock nuts may not be suitable. The all-metal prevailing-torque locking system provides reusable locking performance without a nylon insert, making these nuts suitable for higher-temperature, vibration-prone and inspection-critical applications.

• Small, thin-wall and lightweight construction for aerospace weight saving.
• Reusable all-metal self-locking design with no nylon element.
• MJ and UNJ thread models available for metric and imperial aerospace requirements.
• 12-point nut options allow high torque control in compact assemblies.
• Popular applications include engines, actuators, brackets, accessories and high-temperature hardware.

ALNsbMJ MJ A286 Self-Locking Nuts to EN 3152

ALNsbMJ is an Auto-Lok MJ-thread, single-slotted, prevailing-torque nut manufactured from A286 stainless steel to meet EN 3152 requirements. Designed for aerospace MJ internal threads, it delivers reusable all-metal locking performance with no nylon element, a strength class of 1100 MPa at room temperature and acceptance criteria defined by the EN 3152 delivery standard.

Use ALNsbMJ when the engineering drawing explicitly requires an MJ internal thread, especially where aerospace fatigue behavior, controlled tolerance classes and repeatable locking are important.

ALNsbMJ part numbers

Material, surface finish, classification, thread, tolerances, qualification and acceptance criteria are defined by DIN EN 3152:2005 / EN 3152:2004 for self-locking nuts with MJ thread, manufactured from high heat-resistant steel FE-PA2601 / A286, silver-plated or uncoated, strength class 1100 MPa at room temperature and maximum test temperature of 425 °C.

ALNhsrfMJ Horizontal Slotted Ring Flange Nuts

Auto-Lok HSRF nuts with MJ internal thread profile are horizontal slotted ring flange nuts for aerospace use. These MJ-thread prevailing-torque nuts are suitable for drawings that specify the aerospace MJ internal thread form and require an all-metal locking system.

ALNhsrfMJ part numbers in stock

Titanium MJ-Thread Auto-Lok Nuts

Auto-Lok supplies titanium MJ-thread prevailing-torque nuts for demanding aerospace use. Titanium combines high strength-to-weight ratio with strong corrosion resistance, while the MJ thread form supports improved fatigue performance through its aerospace profile and defined tolerance classes.

Titanium MJ part numbers

Choose titanium MJ nuts when your drawing or standard specifies the MJ thread form, when weight reduction is important, or when thread-root fatigue performance is a key requirement.

ALNmj MJ A286 Self-Locking Nuts

ALNmj nuts are all-metal self-locking nuts with MJ threads in A286 stainless steel, designed for high-temperature and high-load aerospace applications. With a performance level of 1100 MPa and passivated finish, they provide durable, repeatable locking on critical MJ-threaded joints.

These nuts are intended for MJ3 to MJ12 fine-pitch threads and are commonly used on engine accessories, actuators, high-temperature brackets and other aerospace hardware where conventional metric lock nuts are not suitable.

• Material grade: stainless steel A286
• Finish: passivated for improved corrosion resistance
• Performance class: 1100 MPa
• Thread types: MJ3 × 0,5 up to MJ12 × 1,25, with 4H5H or 4H6H tolerance classes

ALNmj A286 part numbers and key dimensions

MS21043 Self-Locking Nut Alternatives

Auto-Lok can produce alternatives to MS21043 self-locking nuts. These parts use threads per MIL-S-8879 style UNJ thread requirements and are suitable where a corrosion-resistant, high-temperature A286 stainless steel distorted-thread flange nut alternative is required.

A286 stainless steel provides higher strength than many common stainless grades and is used for elevated-temperature aerospace fastening applications. These nuts resist corrosion and are suitable for demanding environments where all-metal locking is preferred.

Auto-Lok 12 Point Locking Nuts - ALN12P

Auto-Lok 12-point locking nuts, including the ALN12P range, are used where compact envelope, high strength and accurate torque control are required. A 12-point wrenching design allows higher torque transmission in tight aerospace assemblies compared with many conventional hex configurations.

For applications involving MJ or UNJ thread callouts, confirm the exact drawing requirement, thread class, material, finish and prevailing-torque requirement before selecting the final part number.

ALN12P program

Dimensions are shown in inches, axial strength in pounds-force (lbf), and weight in grams. Full dimensions, torque data and material specifications are available in the catalogue.

Frequently Asked Questions