Fastener Selection for Structural Steel

Choosing the right fastener is critical to the safety, durability, and performance of any steel structure project. With countless bolt grades, coating options, and connection types available, the selection process can feel overwhelming. Yet a poor choice often leads to joint failure, corrosion, or costly rework. This guide breaks down the key factors,strength class, environmental conditions, installation method, and applicable standards,so you can make confident decisions that keep your builds secure and code compliant.

Bolts

Bolts are externally threaded mechanical fasteners, typically featuring a hexagonal head; they are the most widely used type of detachable fastener and are generally used in conjunction with nuts and washers.

Main types and applications:

Hex head bolts: Classified into grades A, B, and C; grades A and B offer high precision and are used in critical load-bearing areas, while large hex head bolts provide a larger load-bearing surface.

Square head bolts: Offer secure gripping; commonly used in rough structures and T-slot installations.

Reamed-hole bolts (fitted bolts): The shank fits tightly into the hole to prevent misalignment of the connected parts.

Anchor bolts: Embedded in concrete foundations to secure equipment frames.

High-strength bolts: Specifically designed for friction-type connections in steel structures such as bridges, buildings, and steel frameworks.

Nuts

Nuts are internally threaded fasteners—most commonly hexagonal in shape—used with bolts or studs to lock components together.

Main types and applications:

Standard hex nuts: Available in various precision grades; thin nuts serve as jam nuts (lock nuts) to prevent loosening, while thick nuts are suitable for applications requiring frequent assembly and disassembly.

Square nuts: Used in conjunction with square head bolts.

Slotted nuts: Used with drilled bolts and cotter pins to provide a dual-locking mechanism against loosening.

Lock nuts: Feature nylon inserts or all-metal locking structures; they offer excellent resistance to loosening and are reusable.

Specialty nuts: Wing nuts allow for manual assembly and disassembly without tools; cap nuts (acorn nuts) are used to cover and protect exposed threaded ends.

Screws

Screws are relatively small fasteners with diverse head styles (flat, countersunk, Phillips, etc.). They are typically screwed directly into pre-threaded holes in the workpiece—rarely paired with nuts—and serve primarily for fastening or positioning.

Main types and applications:

Machine screws: Available in various head and drive styles; Phillips drives resist cam-out (slipping), while hex sockets withstand high torque and allow the head to be recessed, making them suitable for compact assemblies.

Set screws: Used to fix the relative position of parts; tip styles include cone, flat, and dog (cylindrical) points, selected based on workpiece material and load requirements.

Specialty screws: Includes hex socket screws, eye screws, captive screws, and locating screws to meet specific installation needs.

Studs (Double-ended studs)

Studs feature external threads at both ends with a smooth shank in the middle; they come in equal-length and unequal-length varieties. During use, one end is screwed into a thick-walled base, while the other is secured with a nut. They are ideal for thick components, compact structures, and applications requiring frequent disassembly where standard bolts are unsuitable; they also serve positioning and limiting functions.

Wood screws

Designed specifically for joining wood, these feature head styles such as round or countersunk. They are driven directly into the wood to secure the connection, requiring neither nuts nor pre-threaded holes.

Self-tapping screws

These do not require pre-threaded holes; they cut their own threads during installation. They are primarily used for joining materials such as thin sheet metal, plastic, copper, and aluminum. Self-locking variants are also available, offering superior vibration resistance.

Washers

Washers are installed between the fastener (bolt, screw, or nut) and the workpiece surface to provide protection and prevent loosening.

Main types and applications:

Flat washers: Increase contact area, distribute pressure, and compensate for surface irregularities.

Spring washers: Prevent loosening through elasticity and friction; the most common type.

Toothed elastic washers and locking washers: Offer enhanced anti-loosening performance; suitable for vibrating equipment.

Beveled washers: Designed for inclined contact surfaces (such as on I-beams or channel steel) to ensure the fastener is loaded perpendicularly. Retaining Rings

Retaining rings are installed on shafts or within bores to provide axial positioning, locking, or anti-loosening functions for components. Types include elastic retaining rings, wire retaining rings, locking rings, and shaft-end rings; different styles cater to specific load-bearing and positioning requirements.

Pins

Pins primarily serve a positioning function but are also used for fastening and anti-loosening; some types can act as safety devices for overload protection.

Main types and applications:

Cylindrical pins: Secured via interference fit; offer high positioning accuracy but are unsuitable for repeated disassembly and reassembly.

Taper pins: Feature a tapered design for easy installation and self-locking capabilities; suitable for frequent disassembly and reassembly.

Cotter pins: Used in conjunction with slotted nuts and drilled bolts; a classic mechanical component for preventing loosening.

Rivets

Rivets feature an unthreaded shank and an integral head; they form a permanent connection through deformation caused by hammering or squeezing and are classified as non-detachable fasteners. They are categorized by manufacturing process into hot-forged and cold-headed rivets. Hollow or semi-hollow rivets are commonly used to join lightweight components made of materials such as leather, plastic, or wood.

Fastener Assemblies

Fastener assemblies are composite fasteners consisting of a bolt, screw, or self-tapping screw paired with a washer. They are designed so that the washer rotates freely yet remains captive (does not detach). This integrated configuration simplifies the selection and assembly process while ensuring the washer is always included.

Other Fasteners (Weld Studs)

Represented by weld studs (also known as shear studs), this category of fasteners is attached to steel structural bases via welding. They are specialized, non-detachable connectors primarily used in applications such as welded steel connections and shear connections for composite beams.

Principles for Fastener Selection

Standardization

Minimize the variety of fasteners used within a single piece of equipment or project to enhance manufacturing and assembly efficiency.

Cost-Effectiveness and Practicality

Prioritize the use of commercially available standard parts to control costs.

Selection Based on Requirements

Determine the fastener type and grade by considering the application environment, load magnitude, precision requirements, thread specifications, and mechanical properties.

For more information needed or any inquiry,please feel free to contact Yumisteel team.