Skybolt - SkyLoc® Structural Fasteners / SkyLoc® External Thread (EXT) Series / SkyLoc® EXT Studs

QL4S-EXT8

Mon, 5 Jan 2026 11:52:17 GMT

SkyLoc QL4S-EXT Flush Head Extended Thread Stud

100° Countersunk Head | 9/64" Hex Recess | 2-Lead Thread | High-Strength Steel

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.

Specifications

Thread Size:	1/4-28 UNF-3A (2-Lead Thread)
Head Style:	100° Flush Countersunk Head, 9/64" Hex Recess
Material:	4140 Steel (ASTM A322)
Heat Treatment:	180-200 KSI
Finish:	Cadmium Plate per AMS QQ-P-416 Type II, Class 2
Grip Range:	.150" – .850" (dash number dependent)
Thread Type:	Extended Thread Design (EXT Series)
Previous Part Number:	SK21037-X-XHS
Compliance:	AS9100D Certified, CAGE Code 435Z0

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

Component	Part Number	Description
Stud	QL4S-EXT#	Flush head extended thread stud, 9/64" hex (select dash number for grip)
Receptacle	QL4-21	Caged floating receptacle assembly for radial float applications
Retainer	QL4S-RET#	Spring retainer for loose panel applications
Grommet	QL4C-#G	Load distribution and panel protection for flush installations

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)

📏 Grip Selection Guide: Total grip = outer panel thickness + inner structure thickness. Select the dash number (2, 4, 6, 8, or 10) that accommodates your calculated grip range. The extended thread design provides longer thread engagement for applications requiring increased grip capability. Ensure panel counterbore depth accommodates the 100° countersunk head for proper flush installation.

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.

Visit SkyLoc® EXT Studs to see additional products in this category.

QL4S-EXT6

Mon, 5 Jan 2026 11:52:17 GMT

QL4S-EXT6
Buy Now: $34.20

SkyLoc QL4S-EXT Flush Head Extended Thread Stud

100° Countersunk Head | 9/64" Hex Recess | 2-Lead Thread | High-Strength Steel

Technical Overview

Specifications

Thread Size:	1/4-28 UNF-3A (2-Lead Thread)
Head Style:	100° Flush Countersunk Head, 9/64" Hex Recess
Material:	4140 Steel (ASTM A322)
Heat Treatment:	180-200 KSI
Finish:	Cadmium Plate per AMS QQ-P-416 Type II, Class 2
Grip Range:	.150" – .850" (dash number dependent)
Thread Type:	Extended Thread Design (EXT Series)
Previous Part Number:	SK21037-X-XHS
Compliance:	AS9100D Certified, CAGE Code 435Z0

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

Component	Part Number	Description
Stud	QL4S-EXT#	Flush head extended thread stud, 9/64" hex (select dash number for grip)
Receptacle	QL4-21	Caged floating receptacle assembly for radial float applications
Retainer	QL4S-RET#	Spring retainer for loose panel applications
Grommet	QL4C-#G	Load distribution and panel protection for flush installations

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

Visit SkyLoc® EXT Studs to see additional products in this category.

QL4S-EXT4

Mon, 5 Jan 2026 11:52:17 GMT

QL4S-EXT4
Buy Now: $21.81

SkyLoc QL4S-EXT Flush Head Extended Thread Stud

100° Countersunk Head | 9/64" Hex Recess | 2-Lead Thread | High-Strength Steel

Technical Overview

Specifications

Thread Size:	1/4-28 UNF-3A (2-Lead Thread)
Head Style:	100° Flush Countersunk Head, 9/64" Hex Recess
Material:	4140 Steel (ASTM A322)
Heat Treatment:	180-200 KSI
Finish:	Cadmium Plate per AMS QQ-P-416 Type II, Class 2
Grip Range:	.150" – .850" (dash number dependent)
Thread Type:	Extended Thread Design (EXT Series)
Previous Part Number:	SK21037-X-XHS
Compliance:	AS9100D Certified, CAGE Code 435Z0

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

Component	Part Number	Description
Stud	QL4S-EXT#	Flush head extended thread stud, 9/64" hex (select dash number for grip)
Receptacle	QL4-21	Caged floating receptacle assembly for radial float applications
Retainer	QL4S-RET#	Spring retainer for loose panel applications
Grommet	QL4C-#G	Load distribution and panel protection for flush installations

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

Visit SkyLoc® EXT Studs to see additional products in this category.

QL4S-EXT10

Mon, 5 Jan 2026 11:52:17 GMT

QL4S-EXT10
Buy Now: $39.25

SkyLoc QL4S-EXT Flush Head Extended Thread Stud

100° Countersunk Head | 9/64" Hex Recess | 2-Lead Thread | High-Strength Steel

Technical Overview

Specifications

Thread Size:	1/4-28 UNF-3A (2-Lead Thread)
Head Style:	100° Flush Countersunk Head, 9/64" Hex Recess
Material:	4140 Steel (ASTM A322)
Heat Treatment:	180-200 KSI
Finish:	Cadmium Plate per AMS QQ-P-416 Type II, Class 2
Grip Range:	.150" – .850" (dash number dependent)
Thread Type:	Extended Thread Design (ET Series)
Previous Part Number:	SK21037-X-XHS
Compliance:	AS9100D Certified, CAGE Code 435Z0

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

Component	Part Number	Description
Stud	QL4S-EXT(X)	Flush head extended thread stud, 9/64" hex (select dash number for grip)
Receptacle Options	QL4C-ET Series	Caged floating receptacle for extended thread with radial float capability
	Retainer	QL4RT Series	Spring retainer for loose panel applications
	Grommet	QL4G Series	Load distribution and panel protection for flush installations

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

Visit SkyLoc® EXT Studs to see additional products in this category.

QL4S-EXT2

Mon, 5 Jan 2026 10:39:13 GMT

QL4S-EXT2
Buy Now: $21.81

SkyLoc QL4S-EXT Flush Head Extended Thread Stud

100° Countersunk Head | 9/64" Hex Recess | 2-Lead Thread | High-Strength Steel

Technical Overview

Specifications

Thread Size:	1/4-28 UNF-3A (2-Lead Thread)
Head Style:	100° Flush Countersunk Head, 9/64" Hex Recess
Material:	4140 Steel (ASTM A322)
Heat Treatment:	180-200 KSI
Finish:	Cadmium Plate per AMS QQ-P-416 Type II, Class 2
Grip Range:	.150" – .850" (dash number dependent)
Thread Type:	Extended Thread Design (EXT Series)
Previous Part Number:	SK21037-X-XHS
Compliance:	AS9100D Certified, CAGE Code 435Z0

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

Component	Part Number	Description
Stud	QL4S-EXT#	Flush head extended thread stud, 9/64" hex (select dash number for grip)
Receptacle	QL4-21	Caged floating receptacle assembly for radial float applications
Retainer	QL4S-RET#	Spring retainer for loose panel applications
Grommet	QL4C-#G	Load distribution and panel protection for flush installations

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

Visit SkyLoc® EXT Studs to see additional products in this category.