In product development, mechanical fastening plays a critical role during prototyping and production:
Prototypes: Quick assembly and disassembly for iteration.
Production Assemblies: Proven joint reliability, controlled preload, and standardized hardware.
Field-Serviceable Components: Replaceable parts and accessible repairs, which are vital for industries like automotive, medical devices, and industrial equipment.
Mechanical fasteners also strongly support Design for Assembly (DFA) as they enable:
Simplified component interfaces
Consistent assembly processes
Reduced cycle times
Lower tooling costs
Clear paths for automation
While alternative joining methods may be better suited to specific use cases, mechanical fasteners are indispensable in manufacturing due to their strength, versatility, and compatibility with design constraints.
This article will further discuss mechanical fasteners—the common types, applications, design considerations, and typical problems.
What Are Mechanical Fasteners?
Mechanical fasteners are hardware components that join two or more parts by applying tension, compression, friction, or an interference (press) fit. They can be removed, replaced, or permanently deformed depending on the type and application.
Fastener Classification
Fasteners are broadly categorized by their intended lifespan and connection mechanism. But generally fall into the following categories:
Permanent vs. nonpermanent
Permanent: Rivets, some pins, crimped or deformed fasteners
Nonpermanent: Screws, bolts, nuts—intended to be reused
Semipermanent: Threaded inserts, dowel pins, snap fits
Threaded vs. unthreaded
Threaded: Bolts, screws, inserts
Unthreaded: Rivets, pins, clips, snap fits
Understanding Fastener Loads
Engineers must design for the three primary load directions:
Tensile Loads (Axial): Pulling along the axis of the fastener.
Shear Loads: Sliding forces perpendicular to the axis.
Combined Loading: Most real joints encounter both.
For optimal joint reliability, bolts and screws should primarily carry tension (clamping the joint surfaces together), while the joint interface itself carries the shear load via friction between the clamped parts. Poor load-path alignment—where fasteners are incorrectly stressed in shear or where friction is inadequate—is a leading cause of mechanical fastener failure.
