DML FINAL EXAM QUESTIONS | TESTED AND
PROVEN ANSWERS | LATEST UPDATE 2024/2025
100% (GRADE A+)
Pitch Diameter
Ans>> Sometimes called "mean diameter" is the diameter in between the major and minor
diameter. It is the theoretical diameter at which each pitch is equally divided between threads.
Pitch diameter can be thought of as the diameter at which the male and female thread should
meet. It could be thought of as the working diameter.
Name two ways to measure a thread.
Ans>> Thread micrometer or three-wire thread measurement method.
What is the rule of thumb for the length of internal thread to maximize the strength of the bolt?
Ans>> The minimum recommended thread engagement for a screw in an assembly is as much as
the screw diameter; a better assembly will result when 1 1/2 times the screw diameter is used.
Describe when class two fits are used.
Ans>> Class 2 threads are found on most screws, nuts, and bolts used in the manufacturing
industry. Studs used on many types of machines are examples of class 3 fits.
1
,Describe UNC and UNF.
Ans>> UNC stands for Unified National Coarse thread series and UNF stands for Unified
National Fine thread series. Each has its own strengths. Fine is generally stronger in hard materials
and coarse is generally stronger in soft materials.
What is the formula for calculating the OD of a machine screw?
Ans>> The formula is D=number of the machine screw x.013in. + .060in.; D=8 x .013in. +
.060in. = .164in.
What are setscrews used for?
Ans>> Used to secure gears or pulleys to shafts.
When are stud bolts used?
Ans>> Can be used instead of long bolts. Often used to aid in the assembly of heavy parts by
acting as guide pins.
Describe the strength classification system and marking for bolts.
2
,Ans>> The strength grades of bolts are identified by the markings on the heads. The grade
indicates the strength of the fastener. A manufacturer's chart may be used as a guide for proper
torque of fasteners.
Explain two reasons why flat washers are used.
Ans>> Flat washers provide a larger contact area than nuts and screw heads to distribute the
clamping pressure over a larger area.
What is the purpose of a helical spring lock washer?
Ans>> A helical spring lock washer prevents the unplanned loosening of nut and bolt or screw
assemblies. Spring lock washers will also provide for a limited amount of take-up when expansion
or contraction takes place.
When is an internal-external tooth lock washer used?
Ans>> Are used on oversized holes or to provide a large bearing surface.
When are dowel pins used?
Ans>> Are used to achieve accurate alignment between two or more parts.
3
, When are taper pins used?
Ans>> Accurately align parts that have to be disassembled frequently.
When are roll pins used?
Ans>> Are used to align parts. Holes to receive roll pins do not have to be reamed, which is
necessary for dowel pins and taper pins.
What are retaining rings?
Ans>> Retaining rings are used to hold bearings or seals in bearing housings or on shafts.
Retaining rings have a spring action and are usually seated in grooves.
What is the purpose of a key?
Ans>> To transmit the driving force between a shaft and pulley.
When is a woodruff key used?
Ans>> Are used where only light loads are transmitted.
4
PROVEN ANSWERS | LATEST UPDATE 2024/2025
100% (GRADE A+)
Pitch Diameter
Ans>> Sometimes called "mean diameter" is the diameter in between the major and minor
diameter. It is the theoretical diameter at which each pitch is equally divided between threads.
Pitch diameter can be thought of as the diameter at which the male and female thread should
meet. It could be thought of as the working diameter.
Name two ways to measure a thread.
Ans>> Thread micrometer or three-wire thread measurement method.
What is the rule of thumb for the length of internal thread to maximize the strength of the bolt?
Ans>> The minimum recommended thread engagement for a screw in an assembly is as much as
the screw diameter; a better assembly will result when 1 1/2 times the screw diameter is used.
Describe when class two fits are used.
Ans>> Class 2 threads are found on most screws, nuts, and bolts used in the manufacturing
industry. Studs used on many types of machines are examples of class 3 fits.
1
,Describe UNC and UNF.
Ans>> UNC stands for Unified National Coarse thread series and UNF stands for Unified
National Fine thread series. Each has its own strengths. Fine is generally stronger in hard materials
and coarse is generally stronger in soft materials.
What is the formula for calculating the OD of a machine screw?
Ans>> The formula is D=number of the machine screw x.013in. + .060in.; D=8 x .013in. +
.060in. = .164in.
What are setscrews used for?
Ans>> Used to secure gears or pulleys to shafts.
When are stud bolts used?
Ans>> Can be used instead of long bolts. Often used to aid in the assembly of heavy parts by
acting as guide pins.
Describe the strength classification system and marking for bolts.
2
,Ans>> The strength grades of bolts are identified by the markings on the heads. The grade
indicates the strength of the fastener. A manufacturer's chart may be used as a guide for proper
torque of fasteners.
Explain two reasons why flat washers are used.
Ans>> Flat washers provide a larger contact area than nuts and screw heads to distribute the
clamping pressure over a larger area.
What is the purpose of a helical spring lock washer?
Ans>> A helical spring lock washer prevents the unplanned loosening of nut and bolt or screw
assemblies. Spring lock washers will also provide for a limited amount of take-up when expansion
or contraction takes place.
When is an internal-external tooth lock washer used?
Ans>> Are used on oversized holes or to provide a large bearing surface.
When are dowel pins used?
Ans>> Are used to achieve accurate alignment between two or more parts.
3
, When are taper pins used?
Ans>> Accurately align parts that have to be disassembled frequently.
When are roll pins used?
Ans>> Are used to align parts. Holes to receive roll pins do not have to be reamed, which is
necessary for dowel pins and taper pins.
What are retaining rings?
Ans>> Retaining rings are used to hold bearings or seals in bearing housings or on shafts.
Retaining rings have a spring action and are usually seated in grooves.
What is the purpose of a key?
Ans>> To transmit the driving force between a shaft and pulley.
When is a woodruff key used?
Ans>> Are used where only light loads are transmitted.
4
