Technical Overview

The QL4S-EXT extended thread stud is engineered for structural applications requiring a flush-mounted fastening solution with extended grip capability. The 1/4-28 UNF-3A two-lead thread design provides rapid quarter-turn installation while the 100° countersunk head sits flush with panel surfaces for aerodynamic and aesthetic requirements. Manufactured from 4140 steel per ASTM A322 and heat treated to 180-200 KSI, this fastener provides exceptional strength for demanding aerospace, motorsport, and industrial installations. Cadmium plating per AMS QQ-P-416 Type II, Class 2 ensures superior corrosion resistance. Previously designated as SK21037-X-XHS, this stud is interchangeable with industry standard parts.

Applications

• Aerospace: Flush-mounted structural panels, aerodynamic surfaces, wing and fuselage access panels requiring high strength and low profile
• Motorsport: Body panels, aerodynamic fairings, underbody covers where flush mounting is critical for airflow management
• Industrial: Equipment enclosures, control panels, applications requiring smooth exterior surfaces and frequent access
• Marine: Deck hardware, flush-mounted hatches, applications requiring corrosion resistance with countersunk installation
• Defense: Military aircraft structural panels, ground support equipment requiring MIL-SPEC finish and high strength-to-weight ratio

Complete System Components

Key Features

• Extended Thread Design: Longer thread engagement length provides increased grip range capability for thicker panel assemblies
• Flush Mounted Profile: 100° countersunk head sits flush with panel surface for aerodynamic applications and smooth exterior finish
• High Strength Construction: 4140 steel heat treated to 180-200 KSI provides superior tensile and shear strength for structural applications
• Two-Lead Thread: Dual-start thread design enables 180-degree rotation for rapid quarter-turn fastening
• Cadmium Plating: AMS QQ-P-416 Type II, Class 2 finish provides excellent corrosion resistance in harsh environments
• Industry Standard Interchange: Compatible with existing quarter-turn fastening systems (replaces SK21037-X-XHS)

Quality & Compliance

Manufactured by Skybolt Aerospace Fasteners under AS9100D certification at our Leesburg, Florida facility (CAGE Code: 435Z0). All QL4S-EXT studs are 100% inspected to drawing specifications and include full material traceability. Material conforms to ASTM A322 for 4140 alloy steel bar stock with heat treatment to 180-200 KSI ultimate tensile strength. Cadmium plating meets AMS QQ-P-416 Type II, Class 2 requirements for enhanced corrosion resistance in aerospace and military applications.