CFS Fastener Selection & Application 3

Question 1

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

Accepted Answer

Higher resistance to vibration loosening

Answer

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

Question 2

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

Accepted Answer

Pre-drilling a pilot hole

Answer

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

Question 3

Which metric property grade bolt has the highest tensile strength?

Accepted Answer

Grade 12.9

Answer

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

Question 4

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

Accepted Answer

Creating a precise pivot point or guide for moving parts

Answer

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

Question 5

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

Accepted Answer

Galvanic corrosion

Answer

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

(CFS) Certified Fastener Specialist Practice Test