CFS Thread Design & Compatibility 2

Question 1

What does the thread tolerance class 6H/6g denote in the ISO metric system?

Accepted Answer

Standard internal/external thread tolerance for general use

Answer

6H denotes the internal (nut) thread tolerance and 6g denotes the external (bolt) thread tolerance; together they represent the standard general-purpose fit in ISO metric threading.

Question 2

Which thread form has a 60° included angle and is the most widely used in the United States?

Accepted Answer

Unified National thread

Answer

The Unified National (UN) thread form uses a 60° included angle and is the dominant fastener thread standard in the United States.

Question 3

A bolt is specified as 3/8-16 UNC. What does '16' represent?

Accepted Answer

Number of threads per inch

Answer

In the designation 3/8-16 UNC, '16' is the number of threads per inch (TPI), which defines the pitch of the thread.

Question 4

Which condition describes the maximum material condition (MMC) for an externally threaded fastener?

Accepted Answer

Largest pitch diameter allowed

Answer

For an external thread, MMC corresponds to the largest allowable pitch diameter, meaning the most material is present on the bolt.

Question 5

What is the primary reason UNF (fine thread) fasteners are preferred over UNC in high-vibration aerospace applications?

Accepted Answer

Greater tensile strength per unit length and better self-locking tendency

Answer

UNF threads have a smaller pitch, increasing the number of threads per inch, which raises the stripping torque threshold and resists vibration loosening better than coarse threads.

(CFS) Certified Fastener Specialist Practice Test

(CFS) Certified Fastener Specialist Practice Test

CFS Thread Design & Compatibility 2