Complete Guide to Bolts: Types, Applications & Selection

Hex bolts are the most common industrial bolts, featuring a six-sided head for wrench tightening. Standard hex bolts come fully threaded, while hex bolt half threaded variants have threads only on the lower portion with a smooth shank. Half-threaded hex bolts are ideal for applications requiring precise clamping where the smooth shank prevents thread galling and provides better shear strength. Both types are available in mild steel (MS), stainless steel SS304, and high-tensile grades. Common sizes range from M6 to M24 for general applications, with larger sizes M30-M48 for heavy machinery. Hex bolts are widely used in structural steel connections, machinery assembly, automotive suspensions, and heavy equipment.

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Allen bolts (socket head cap screws) feature a cylindrical head with internal hexagonal socket, allowing high torque application in confined spaces. Their low-profile design and superior strength-to-weight ratio make them preferred in machinery and automotive applications. Allen CSK (countersunk) bolts have a conical head that sits flush with the surface, ideal for applications requiring smooth finishes without protruding heads. Both types provide clean aesthetics and space efficiency. Allen bolts are manufactured in grades 8.8, 10.9, and 12.9 (strength grades), with SS304 and SS316 variants for corrosion-resistant applications. Common sizes include M3, M4, M5, M6, M8, M10 for machinery assembly, robotics, automotive engine components, CNC machines, and precision equipment.

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U-bolts are bent into a U-shape with threads on both ends, used for clamping round or rectangular objects like pipes, tubes, and beams. They're essential in automotive suspensions for securing leaf springs and axles, plumbing for pipe supports, electrical installations for conduit mounting, and marine applications for securing railings and rigging. T-bolts have a T-shaped head that slides into T-slot channels (common in machine tables, aluminum extrusions, and modular workstations), providing adjustable mounting without drilling. J-bolts feature a J-shaped hook on one end with threads on the other, used for anchoring equipment to concrete foundations, securing wooden structures to masonry, and hanging applications. All three types are available in mild steel zinc-plated, hot-dip galvanized for outdoor use, and stainless steel SS304/SS316 for corrosive environments.

Carriage bolts feature a rounded head with a square neck beneath, designed for wood-to-wood or wood-to-metal fastening. The square section prevents rotation when tightening the nut, eliminating need for holding the bolt head. Widely used in wooden structures, furniture assembly, deck construction, and playground equipment. Coach bolts are similar but typically refer to larger sizes used in heavy timber framing and coach-building applications. Button head bolts have a low, rounded head with internal hex socket, providing aesthetic appeal and smooth surface finish. These are popular in furniture, automotive interiors, architectural applications, and anywhere a decorative, low-profile fastener is needed.

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Flange bolts have an integrated flange (washer) under the head, distributing load over a larger area and eliminating need for separate washers. This design saves installation time and ensures consistent clamping pressure. Used extensively in automotive engine assembly, transmission mounting, suspension components, and machinery where vibration resistance is critical. Flange button head bolts combine flange benefits with button head aesthetics, providing smooth rounded appearance with enhanced load distribution. Dome bolts feature a hemispherical head for decorative applications where appearance matters, commonly used in furniture, architectural fixtures, and visible fastening points.

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Eye bolts have a circular loop at one end for attaching cables, ropes, or chains, essential in lifting applications, rigging, cable management, and suspension systems. Available in forged carbon steel for heavy lifting and stainless steel for marine use, with working load limits clearly marked. Hook bolts feature a hook shape for hanging applications, cable routing, and suspended loads. Wing bolts have wing-shaped heads for hand-tightening without tools, perfect for frequently removed panels, adjustable equipment, and tool-free assemblies. Shoulder bolts (stripper bolts) have a smooth, precise-diameter shoulder section acting as a rotating shaft or precision spacer in mechanisms, fixtures, and automated equipment. Nylon hex bolts are lightweight, non-conductive, corrosion-proof alternatives for electronics, chemical equipment, food processing, and applications requiring electrical insulation or non-scratching properties.

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