Classic cars forum & vehicle restoration.

[Rich5ltr]

Well bolts and screws actually; would someone define a bolt (in engineering terms) as opposed to a screw. I always think of screws as having a thread all the way to the top and a bolt as having a non-threaded section up to the head. However looking at many web sites, like Screw-fix, it seems that the general usage these days is that a screw is what you use to put a few shelves up with and generally goes into wood o(obviously not if it's a self tapper but you get my drift) and a bolt is anything that you screw into a lump of metal like an engine or a car, regardless of whether it has a nut on the end or not Help...

[buzzy bee]

Hi

If you put the word "set" before the word "screw" it all changes! he he

Bolts are partially treaded, set screwes are fully threaded. In my understanding.

Then again on:- http://euler9.tripod.com/bolt-database/boltdef.html

It says:-

The extent to which the shank of a fastener is threaded, whether fully or partially, does not affect the above definition in any way. Bolts can come fully or partially threaded, as do screws.

Whether or not a nut is installed does not affect the above definition in any way. Common sense tells you a bolt is not suddenly metamorphosed into a screw each time you extract the nut (if you chose to install a nut instead of using the bolt in a threaded hole, insert, or nutplate); nor is it suddenly transformed into a screw each time you choose to not use the bolt but just let it sit there on a table unused.

Bolts are untapered. Screws are often tapered but can also be untapered.

Screws always cut their own internal threads when initially installed, as there is generally no tool meeting the arbitrary specification of their threads to tap out the internal threads beforehand. Conversely, however, it is possible for a bolt to be self-tapping. The only criterion in regard to the bolt versus screw definition is whether or not the self-tapping fastener, non-cutting threads meet the strict specification of bolt threads, meaning they can be correctly mated with a nut.

The type or size of head on a fastener does not affect the above definition in any way. Bolts come with almost every imaginable head; screws do also, including hexagonal. Likewise, the configuration of the driving (or holding) tool surfaces in the head, whether internal or external surfaces, does not affect the above definition in any way.

The fastener nominal diameter does not affect the above definition in any way. Bolts do not suddenly and mysteriously no longer accept nuts just because they become small, miniature, or micro.

The term "machine screw" is a misnomer. A bolt, clearly having bolt threads, is not suddenly metamorphosed into a screw just because someone arbitrarily misnamed it in a specification, book, organization, or industry.

Whether or not specifications incorrectly or loosely refer to bolt and nut threads as "screw threads," or even erroneously refer to bolts as "screws," does not suddenly transform the bolt into a screw. The inability of the technician who drafted the specification to master or understand language, grammar, measurement systems, coherent, unambiguous, internationally-standard units of measure, correct mathematical expressions, etc., does not mean the coherent engineers are suddenly thrown into an abyss without coherent definitions. Intelligent engineers must be able to sort out the technical facts from among the fiction and typos. Whenever someone has botched definitions, world class organizations such as ISO and IEEE need to step up to the plate and redirect the incoherent, aimless, arbitrary, lower-level entities. All of these incorrect definitions and misuses of the word "screw" should be completely ignored, as there is no need to continue to copy past mistakes and propagate confusion. The previously-stated, correct definition should be used in new specifications, standards, and publications.



Cheers

Dave

[Penman]

Hi
But machine screws have parrallel threads.
I would have said that a Bolt requires a spanner either on the bolt head and nut or nut only in the case of a coach bolt.
Whereas a screw requires a screwdriver of some sort Slot/Phillips/Posidrive/Torx/Hex etc which fit into a recess in the screwhead.
_________________
Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10

[Phil - Nottingham]

In engineering terms the term Setscrew I have always taken is a bolt that is fully threaded although they can have a variety of heads
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Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2

[P3steve]

You guys need to get out more!