S-99638A200 1/4"-28 MS21045-4 Locknuts

Key Features & Benefits at a Glance

• Superior vibration resistance through flex-top locking technology that maintains clamp force under dynamic loads
• Enhanced corrosion protection with cadmium yellow-chromate plating for extended service life in harsh environments
• Precision thread engagement with Class 3B fit ensuring reliable performance in critical applications
• Industry-standard compliance meeting MS21045-4 specifications for consistent quality and interchangeability
• Optimized installation with standard external hex drive for easy wrench access and proper torque application
• Fine thread advantage with 1/4"-28 UNF providing better adjustment control and load distribution
• Dimensional reliability with 7/16" hex width and 5/16" height for consistent fit in standard applications

Professional Applications & Engineering Value

This MS21045-4 compliant locknut delivers critical vibration resistance in demanding industrial and aerospace applications where safety and reliability are paramount. The flex-top locking mechanism creates consistent friction against mating threads, preventing loosening under extreme vibration and thermal cycling. Manufactured from cadmium yellow-chromate plated steel, this external hex locknut provides superior corrosion protection while maintaining electrical conductivity. The Class 3B thread fit with UNF fine-pitch threading ensures precise engagement and uniform load distribution, making it ideal for aircraft assemblies, heavy machinery, and precision equipment where vibration-resistant fastening is essential for operational safety and reduced maintenance intervals.

Specification Summary & Compliance

This 1/4"-28 UNF locknut features precision Class 3B thread fit with right-hand fine-pitch threading, ensuring exact dimensional accuracy per industry standards. The component strictly adheres to MS21045-4 military specifications for quality and performance verification. With a standard hex profile measuring 7/16" across flats and 5/16" height, this inch-system locknut provides consistent dimensional stability. The cadmium yellow-chromate plating meets environmental compliance standards while delivering superior corrosion protection for extended service life in demanding operational conditions.