Threaded & Locking Devices

Question 1

Other than safety shoes and glasses, what other types of personal protective equipment should be worn in a loud atmosphere with work being done overhead? List 3 examples.

Answer 1

Gloves

Earplugs

Hard hat

Question 2

Where would you find the grade of a metric bolt and nut? What would you want to look for exactly?

Answer 2

Metric fasteners indicate property class with numbers. The higher the class number the higher the tensile strength.

Question 3

What is a good reason to maintain good housekeeping in your work area? List 3 reasons.

Answer 3

Tripping hazards can be avoided if walkways are kept clear of boxes, parts, pallets and tools.

Oil spills should be cleaned up immediately to avoid slips or falls.

Access to electrical panels, fire extinguishers and exits must be kept clear of obstacles.

Good housekeeping creates a safe workplace and improves productivity.

Question 4

What is the difference between a screw and a bolt?

Answer 4

A bolt is any fastener used with a nut and is tightened and released by applying torque to the matting nut. A screw is different from a bolt because it mates with an internal thread. The difference between screw and bolt is its application.

Question 5

What is a plow bolt? Name one application

Answer 5

Plow bolts are designed to hold the plowshare to the moldboard. The head is countersunk with a square shoulder. It sits flush to allow dirt or gravel to pass easily. Plow bolts are used on many types of heavy construction equipment, such as snowplows, road graders, and scoop shovels.

Question 6

What is the main advantage when selecting an elevator bolt for a specific application? Also state the possible application.

Answer 6

Elevator bots were originally designed for attaching elevator buckets to conveyer belts, elevator bolts are similar to carriage bolts, except the head is thin and flat. Elevator bolts have a square neck that resists turning when the nut is tightened or remover. The large head provides a greater bearing surface for soft materials. Elevator bolts are used in grain elevators and other conveyer systems.

Question 7

What are the two systems, Metric and Imperial, ways to determine the strength of a hex head cap screw?

Answer 7

The markings found on bolt head indicate the fasteners grade or property class. Both grade and class refer to the tensile strength of the bolt. Imperial standard bolts are marked with lines to indicate grade or they may be blank. Metric fasteners indicate property class with numbers.

Question 8

When measuring the length of a socket head cap screw vs a flat head cap screw, where would you properly measure the overall length?

Answer 8

Overall length of flat head cap screw is total length of the screw, top of the head to the end of the thread. Overall length of socket head cap screw does not include head length, measure from the bottom of the head to the end of the thread.

Question 9

What style of nut is held in position with a cotter pin?

Answer 9

Castellated nut

Question 10

Acorn nuts serve one main purpose, this is to _______________________.

Answer 10

Protect the thread or to protect nearby objects from contact with the thread.

Question 11

Hex nuts can be found in different thicknesses. What is the purpose of the hex nut that is thin? Give an example of where you would find/use this style of nut.

Answer 11

Jam nuts are thinner than regular hex nuts and are paired with hex nuts to lock them in position. Jam nut is often used when a nut needs to be locked in place without clamping against another object. The jam nut essentially acts as the “other object” as the two nuts are tightened against each other. Jam nuts are also used as a locknut to prevent vibration from loosening a bolted joint. Used in steering locking tie rod end in place. Used in vibration bowl to prevent nuts from loosening.

Question 12

Nylon lock nuts differ from a prevailing torque lock nut. What is this obvious difference?

Answer 12

All metal lock nuts are also called distorted thread nuts or crimp nuts because the locking action is created by crimping the nut to cause a distortion in the threads. The distorted thread creates a prevailing torque due to what is known as the interference thread fit. Meaning, the threads within the nut are designed to grab hold of a mating bolts threads when installed which creates the locking action.

Nylon insert lock nuts create their locking action from a nylon ring that is inserted into the top of the nut. When a nylon insert lock nut is mated with a receiving screw, the nylon will then compress around the threads, creating a secure lock between both the nut and screw.

Question 13

How many times should you use these nuts from question 11? (Not found in your module)

Answer 13

Only use one time

Question 14

How are machine screws determined?

Answer 14

Machine screws are smaller than machine bolts, usually less than ¼” in diameter and never larger than ¾”. Machine screw dimensions are given with two numbers separated by dash. The first number indicates the screw’s diameter the second indicates thread pitch.

Question 15

List the three most commonly used drivers for the different machine screws.

Answer 15

Standard, keystone or slotted
Phillips cross slot
Robertson

Question 16

Give three examples of where you would use a set screw and four different set screw point styles?

Answer 16

Uses:

Hub
Collar
Gear
Sleeve

Point styles: 
Knurled point 
Flat point 
Oval point 
Cone point

Question 17

Which style of set screw would you want to use on a application that does not need a lot of “grip” and also does the lease amount of marring to the surface?

Answer 17

Oval point set screw

Question 18

For ease of assembly/disassembly, what should you do to the shaft before screwing a setscrew onto it to hold it in position? What is another consideration when drilling and tapping your set screw hole into the hub?

Answer 18

For ease of assembly and disassembly, it is good practice to file a small flat under the point of the set screw. It is good practice to use two set screws set at 90° to each other. When considering drilling and tapping another hole for set screw, set it 90° from first hole.

Question 19

What is a stud? Give a common application.

Answer 19

Studs are cylindrical shafts that are threaded on both ends. One end of the stud, called the metal end, is threaded into a workpiece. The other end, called the nut end, passes through a clearance hole in a mating part. A nut is then used to tighten the assembly together. Used on milling machine to clamp work piece to the table.

Question 20

What is the difference between a thread forming screw and a thread cutting screw? Give three types of each.

Answer 20

Thread-forming screws are used to assemble sheet metal, plastics and soft metals, such as brass and aluminum. The screw forms a thread by displacing or rolling the material. No cutting occurs and the thread material adjacent to the screw pilot hole wraps around the threads. Types : A, AB, B and C

Thread-cutting screws cut a thread in the parent material, which can be aluminum, zinc, steel sheet, cast iron, brass or plastic. The thread form is very similar to a machine screw thread. Types: BG, BT, D and T

Question 21

List three commonly used anchors used in industry and write a short explanation of how they work?

Answer 21

Lead screw anchors are resilient lead alloy anchors that conform to uneven surface to provide a gripping action. The flanges are set by placing a pipe over the bolt and into the hole. When you strike the pipe, the lead anchor spreads the flanges out to the hole wall where they grip.

Expansion shields for machine bolts and lag screws are designed to expand as the screw is screwed into the anchor, thus giving the holding power.

Toggle bolts are machine screws with spring-loaded, double-flanged anchors for securing in hollow walls. Toggle bolts require a relatively large hole to pass the anchor through.

Question 22

A special bolt that has jack-bolt built into them for setting a preload is referred to as?

Answer 22

Multi-jackbolt tension bolts

Question 23

What could be used to repair a stripped-out thread?

Answer 23

Threaded inserts are used to repair damaged internal threads.

Question 24

Define the following terms:

Nominal size

Answer 24

The size used for identifying the thread

Question 25

Unified thread classes have codes to which a specific fit tolerance is achieved. If you required a very tight fit for assembling some sort of precision equipment what class would you use?

Answer 25

Classes 3A and 3B

Question 26

What is a reason that you would mix two different classes of hardware together for assembling a part?

Answer 26

To achieve desirable fit.

To achieve desirable mechanical failure – whenever bolts and nuts are subject to enough force, sooner or later, something must fail. Desired failure is the complete fracturing of the bolt or screw, instead of stripping of internally threaded component.

For easier assembly.

Question 27

How are metric threads classed?

Answer 27

In ISO metric fits, tolerance grades and tolerance positions combine to make tolerance classes.

Question 28

How is a metric pitch diameter described in ISO metric system?

Answer 28

The pitch diameter is known as the effective diameter in the ISO metric system.

Question 29

In the metric system they have a tolerance position letter that describes the tolerance (+/-) of a bolt or nut. How would you know, from a description alone that you’re dealing with a nut or a bolt? What is the unified conversion for a tolerance grade of 6?

Answer 29

Screws and bolts can be identified from a description alone by letters, capital letters for nuts, lower case letters for screws.

A tolerance grade of 6 is roughly comparable to the Class 2 tolerances in the unified system.

Question 30

Where would you find the grade of a imperial bolt and nut? What would you want to look for exactly?

Answer 30

The markings found on bolt heads and nuts indicate the fastener’s grade or property class. Both grade and class refer to the tensile strength of the bolt. Look for tensile strength; in imperial system the higher number of lines the higher the grade. Grade markings on bolts allow you to judge the amount of torque that a particular bolt may receive. The lower the grade of the bolt, the less torque can be applied. Grade markings on nuts present a means of matching a nut and bolt.

Question 31

Define the following terms:

Maximum metal condition

Answer 31

Where the pitch diameter of the external thread is the largest allowable and that of the mating internal thread is the smallest allowable.

Question 32

Define the following terms:

Allowance

Answer 32

The intentional difference in size between mating threaded parts at maximum metal condition. The amount of allowance determine the type of fit.

Question 33

Define the following terms:

Fit

Answer 33

A general term that specifies the intended degree of tightness or looseness between mating threaded parts.

Question 34

Define the following terms:

Tolerance

Answer 34

The amount by which a particular dimension can vary from the design size and still be acceptable.

Question 35

Define the following terms:

Limits of size

Answer 35

The largest and smallest sizes a dimension can be and still be acceptable.

Question 36

Define the following terms:

Actual size

Answer 36

A measured size. It is what the threaded part measures when you check it with a micrometer.