The LD-400 carbon steel set screws, also known as grub screws, are headless threaded fasteners designed to secure one component to another by applying clamping pressure through the screw tip rather than through a conventional head. Unlike standard bolts and screws that clamp via a bearing surface under the head, set screws are fully threaded and driven entirely into a tapped hole using a hex socket (Allen) key, with the screw tip bearing against a shaft, hub, collar, or mating surface to prevent relative movement. This makes set screws the standard fastener for locking pulleys, gears, couplings, knobs, and collars onto shafts, where a protruding head would interfere with assembly or rotation. The Class 45H carbon steel hardness provides the strength needed for the point to indent and grip the shaft surface without deforming under torque transmission loads.

The assortment includes four point types, each engineered for specific fastening and functional requirements. Cup point set screws feature a recessed, cup-shaped tip that provides excellent holding power with minimal shaft damage, making them the general-purpose choice for securing components to smooth shafts. Flat point set screws have a flat bearing surface that distributes load over a larger area for applications requiring repeated adjustments without marring the shaft, and for use on shafts with pre-machined flat spots. Cone point set screws feature a sharp pointed tip that bites into the shaft material for maximum holding torque in high-vibration and permanent installations, though the indentation makes subsequent adjustment and removal more difficult. Dog (full-dog) point set screws have a cylindrical pilot tip that locates precisely into a mating hole or slot, functioning as both a locator and a retainer for alignment and axial positioning applications.

The black oxide finish provides a thin, conversion-coating surface treatment that offers mild corrosion resistance while preserving the precise dimensional tolerances of the threaded components. Unlike heavy plated coatings, black oxide adds negligible thickness to the surface, ensuring the hex socket and thread dimensions remain within DIN 913 specifications for reliable engagement and interchangeability. The matte black appearance is aesthetically uniform and non-reflective, which is preferred in machinery, instrumentation, and applications where appearance matters. Black oxide also provides a clean, dry surface that will not flake or chip like plated coatings, and the finish can be supplemented with a rust-preventative oil for additional corrosion protection in storage and sheltered indoor service.

In shaft and collar fastening applications, set screws are typically installed in radially tapped holes in hubs, collars, and coupling halves, with the screw tip bearing directly on the shaft surface or into a machined flat or groove. For maximum holding power and to prevent shaft damage in critical applications, two or more set screws are often installed at 90-degree or 120-degree offsets around the hub circumference, distributing the clamping force and improving resistance to slippage under torque. The hex socket drive allows the screw to be fully recessed below or flush with the hub surface, providing a compact, unobtrusive fastening solution that does not require external clearance for a wrench. Optional zinc plating and stainless steel 304/316 grades extend the range to corrosion-resistant and food-grade applications where black oxide carbon steel would be unsuitable.