Theory – Fasteners & Locking Devices

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Last updated: May 17, 2019
What is used to transmit a heavy load between a shaft and pulley?
A gib-head key
What is the minimum engagement of a screw?
They have a minimum engagement of 1.5x the diameter of the fastener
What kind of machine screw head style requires a countersunk hole? What is the angle of this countersink?
Flat Head Screws require a countersunk hole at 82 degrees
What are the 3 standard styles of set screws?
The 3 standard styles are Cup Point, Flat Point and Cone Point.
Cap Screws are _____ driven.
Cap Screws are Internally driven
What are half-dog and full-dog set screws used for?
They are used for alignment between a collar and shaft.
What is the difference between a screw and bolt?
A bolt requires a mating nut.

They also have different application.

What do the numbers indicate on metric bolts and screws?
The last two numbers indicate the yield point which is a percent of the ultimate tensile strength. The first number(s) designate the ultimate tensile strength.
What style of self locking washer has a higher holding power? What are some downsides?
The external self locking washer has more holding power than the internal equivalent.

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The downside is the external has reduced appearance, can snag and may be a safety concern.

What is the purpose of flat washers?
To distribute pressure, protect a surface from wear and to act as a spacer.
How are woodruff keys identified?
With a 3 or 4 digit number. The last two digits give the nominal key diameter in eights of an inch and the first digits give the width in 32nds of an inch. Example : a 1418 woodruff key would be 14/32″ width and 18/8″(2 1/4″) diameter.

A dowel pin is made of _____ steel, and is ground to ______ inch over it’s nominal diameter.
A dowel pin is made of hardened steel, and is ground to 0.0002 inch over it’s nominal diameter.
What makes a Pratt and Whitney key easier to align the hub and the key?
The rounded ends help with this.
What is a key used for?
A key is used to mate a hub with a shaft. It’s purpose is either to align or be a shear point.
What are cotter pins used for?
They are used to keep other fasteners in place.

How much over nominal size are radial locking/spring pins?
About 0.003″
Before installing retaining/snap rings what should you refer to?
You should refer to manufacturing specifications.
What are snap/retaining rings used for?
Snap/retaining rings provide a removable shoulder to locate, retain or lock components accurately;y on shafts, bores and inside housings.
Why are acorn nuts used?
For safety and when appearance is important.
What type of Nuts require cotter pins to lock them in place?
Hex Castle and Hex Slotted(Standard, Thick Slotted & High Slotted)
Machine Screws are rarely more than ___ in diameter
Machine Screws are rarely more than 1/4″ in diameter
What is the purpose of a dowel pin?
They are used to align parts during assembly.

They are not meant to hold them in place.

What is the relation to the grade of a bolt/screw to the number of lines on the end? What grade is an exclusion to this rule?
For every line on the end of the bolt/screw add 2 to that number and you will have the grade of bolt. (i.e. 5 marks is a grade 7, 3 marks is a grade 5) The exception to this rule is a grade 3 bolt as it only has 2 marks and a bolt with no marks has a grade of 1.
What type of head is common in woodworking/sheet metal?
The Robertson (Square)
What shape is a Pratt ; Whitney key?
It is a key with rounded ends.
How are tapered pins sized?
They are sized by the length and the major diameter.
What do cotter pins work with?
They work with clevis pins, castle nuts and slotted nuts.
What is the OD of a #6-28 UNC Machine Screw?
OD = # x 0.013 + 0.060OD = 6 x 0.013 + 0.060OD = 0.138″
What key is used on the end of a shaft?
A Gib-Head Key
What is the taper of a tapered dowel pin?
1/4″ TPF
What is the taper of a gib-head key?
1/8″ TPF

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