Fastener Selection & Application Flashcards

What is the primary advantage of using a fine thread (UNF) over a coarse thread (UNC) bolt in the same diameter?

Answer: Higher resistance to vibration loosening

Fine threads have a smaller helix angle, which provides better resistance to self-loosening under vibration due to more thread engagement per length.

A self-drilling screw (also called a Tek screw) eliminates which installation step compared to a standard screw?

Answer: Pre-drilling a pilot hole

Self-drilling screws have a drill-point tip that simultaneously drills and taps the mating material, eliminating the need to pre-drill.

Which metric property grade bolt has the highest tensile strength?

Answer: Grade 12.9

Metric property class 12.9 has a minimum tensile strength of 1220 MPa, the highest of the common metric bolt grades.

In which application would a shoulder bolt (stripper bolt) be the most appropriate fastener choice?

Answer: Creating a precise pivot point or guide for moving parts

Shoulder bolts have an unthreaded cylindrical shank that provides a precise bearing surface for rotating or sliding components.

When fastening dissimilar metals, which primary concern must be addressed to prevent premature failure?

Answer: Galvanic corrosion

When dissimilar metals are in contact in the presence of an electrolyte, galvanic corrosion occurs as the less noble metal corrodes preferentially.

A wood screw and a sheet metal screw of the same size differ primarily in which way?

Answer: Thread form and pitch

Wood screws have coarser threads with a tapered shank, while sheet metal screws have sharper, finer threads that cut into thin metal material.

Which type of washer is specifically designed to prevent galvanic corrosion between a fastener and the substrate?

Answer: Isolating (isolation) washer

Isolating washers are made of non-conductive materials (such as nylon or neoprene) that electrically separate the fastener from a dissimilar metal substrate.