Overview

Carbon steel black socket set screws with cup point, often simply referred to as cup point grubs screws, are headless fasteners designed for secure and permanent fastening applications. The distinguishing feature is their “cup point,” a concave impression at the end of the screw, which “bites” into the mating surface (typically a shaft). This creates a highly resistant frictional lock against axial and rotational movement. Made from carbon steel and typically finished with black oxide, these screws offer high strength and a degree of corrosion resistance suitable for many industrial environments.

Definition

A Carbon Steel Black Socket Set Screw With Cup Point (Grub Screw) is a headless, fully threaded fastener with an internal hexagonal drive (socket) and a concave, cup-shaped point at one end. This cup point is designed to dig into or seat firmly against a shaft or other mating surface, providing a strong, vibration-resistant lock. Manufactured from hardened carbon steel and often treated with a black oxide finish, they are used for high-strength, flush-mounted fastening where a positive grip is required.

Key Features

• Headless Design: Allows for flush or recessed installation, providing a clean appearance and preventing snagging.
• Internal Hex Drive: Utilizes an Allen key (hex wrench) for precise and secure tightening, offering excellent torque transmission.
• Cup Point: The concave point provides a concentrated contact area that digs into or conforms to the shape of a shaft, creating a strong, “biting” grip that resists loosening due to vibration or torque.
• Carbon Steel Construction: Made from high-strength carbon steel, often heat-treated, to withstand significant shear forces and prevent stripping.
• Black Oxide Finish: Provides a mild corrosion resistance (primarily aesthetic and light protection) and reduces light reflection, giving a black appearance.
• Full Thread: Typically fully threaded for maximum engagement within the tapped hole.

Applications

• Shaft Locking: Widely used to secure gears, pulleys, sprockets, and collars onto shafts, providing a positive lock against rotation and axial movement. The cup point bites into the shaft, preventing slippage.
• Motion Control Systems: Critical in robotics, automation, and precise machinery where reliable attachment to rotating components is essential.
• Jigs and Fixtures: Employed in manufacturing jigs, fixtures, and tooling where parts need to be rigidly held in place.
• Automotive and Aerospace: Used in various assemblies where high-strength, vibration-resistant fastening is required for internal components.
• Industrial Machinery: Found in motors, pumps, conveyors, and other heavy equipment for securing rotating or oscillating parts.

Advantages

• Superior Holding Power: The cup point’s ability to “bite” into the shaft provides a very strong and vibration-resistant frictional lock, significantly reducing the chance of loosening.
• Vibration Resistance: Excellent for applications with dynamic loads or vibration, as the positive engagement of the cup point helps maintain the connection.
• Flush Installation: The headless design ensures the screw is fully recessed, creating a compact and snag-free assembly.
• High Strength: Hardened carbon steel construction ensures the screw can withstand substantial torque and shear forces without deformation or failure.
• Cost-Effective: Generally more economical than stainless steel options for applications where extreme corrosion resistance is not the primary concern.
• Reliability: Offers a dependable and robust fastening solution for critical mechanical connections.