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Bolt use - threaded vs plain shank


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Like many of us I have followed BFG’s postings and he has set a question running in my mind about bolt use. 
I use this term “bolt” generically being the hex head long threaded part rather than the nut. 
they seem to be fully threaded or part threaded and part smooth.

my question is 

is there a rule of thumb as to when each type is used?

 

simple plain English guidance needed. Thanks. 

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1 minute ago, Hamish said:

Like many of us I have followed BFG’s postings and he has set a question running in my mind about bolt use. 
I use this term “bolt” generically being the hex head long threaded part rather than the nut. 
they seem to be fully threaded or part threaded and part smooth.

my question is 

is there a rule of thumb as to when each type is used?

 

simple plain English guidance needed. Thanks. 

As far as I know and I stand to be corrected a bolt, ie with a blank shoulder, will also act as a dowel of the exact dimension, whereas a threaded ‘ screw’ will not do this. Also the tensile strength is often higher on a bolt than a screw.

Kevin

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As Kevin states the difference between a bolt and a screw (thread all the way) is the fit and ultimate strength.  A bolt is always preferable as there is far less chance of fretting in the hole so eliminating damage to the components.  It is however always essential to ensure the threaded portion is long enough to establish a full clamping force of the nut or tapped hole.

Neil

 

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Hi Hamish,

the head does not make it a bolt or a screw.

We usually see a hex head on our bolts and screws but they could also have Bi-Hex, Pan heads etc etc.

Also the size does not matter.  A very small  8/40 UNF with plain shank is still a bolt  and if it has threads all the way up it is a screw.

 

Roger

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Thanks

so what governs which is used

screw or bolt

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Hard Line:

Screws are a bodge. Use a bolt with the correct length of plain shank.  
There are applications where screws are preferable but not many. 
 

Reality:

Screws are ok for lightly stressed applications or holding thin components where the shank of a bolt would be minimal. Using screws saves carrying stock of all the different shank lengths. 

Edited by Drewmotty
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I have search Civil Aircraft Inspection Procedures Part 1 in sect BL/2-3 onwards ( Roger will have his own set too no doubt) and only found a written comparison of screws and bolts which is quite woolly and refers only to a particular series of screws.   see image.

As stated above screws are for lightly stressed things bolts do a job of not only clamping but are resilient in sheer and or tension.   This will vary with material the fastener is made from and it’s head design.

 

5D6C4622-54D0-4C9E-87C1-97DA4B87E4DC.png

Edited by BlueTR3A-5EKT
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The excellent Moss catalogs show what bolts and set screws are used in their pictorial diagrams and I tend to follow that. I change the rear lever arm set screw to 2" and nyloc the other side which now prevents the shocker from coming loose.

Regards Harry

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Thanks for the input guys. 
learning all the time. 
:D

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