Socket Head Cap Screw

A socket head cap screw is a threaded fastener with a cylindrical head and an internal hexagonal drive. This design allows for high clamp loads while requiring less head clearance than many other fastener types, making it suitable for machinery and fixtures where space is limited. The internal hex drive provides positive torque transmission and reduces the risk of cam-out compared to slotted or Phillips drives. These screws are commonly used in applications requiring reliable fastening under dynamic or static loads. When specifying a socket head cap screw, buyers must define the thread size and pitch, nominal length, head dimensions, socket size, property class, material, and finish. The applicable standard, such as ISO 4762, governs the dimensional and mechanical requirements, but it does not make sizes, materials, or finishes interchangeable across manufacturers. Therefore, the request for quotation (RFQ) should reference the exact standard or drawing, specify the required configuration, quantity, and any required inspection evidence. Materials on file include alloy steel and stainless steel, but the actual material grade and strength must be confirmed against the selected standard and supplier documentation. Surface finishes may include black oxide, zinc-plated, plain, or other specified coatings, but the suitability of a finish for a given environment must be verified. Always confirm model-specific values and standards with the legal manufacturer or supplier before procurement.

Torque applied through the internal hex drive produces bolt tension and clamp load at the joint. As the screw is tightened, the thread engagement converts rotational force into axial tension, which stretches the screw slightly and creates a clamping force on the components being fastened. This clamp load holds the joint together and resists separation under external loads. The internal hex drive allows for efficient torque transfer and enables the use of wrenches or drivers that fit precisely, reducing the risk of slippage. The relationship between applied torque and resulting tension is influenced by friction at the thread and under the head, so proper lubrication and surface finish are important for achieving the desired preload. Over-tightening can cause thread stripping or screw failure, while under-tightening may result in insufficient clamp load and joint loosening.