Bolt and screw definitions.

[Dave Plowman (News)]

Came across this site when checking on something and it may be of use to others too. Dunno if it's definitive, of course.

[Dave Baker]

referring to it for years. One of their many interesting articles is on helical spring lock washers which are used on all sorts of things but are proven in tests to actually speed up the rate of bolt loosening. I never liked the things even before I came across the site. I always had my doubts if they did any good because critical fasteners like big end or main bearing cap bolts never use them and when they're new the sharp edges always chew up whatever you're bolting to. Anyway since seeing this info I remove them from anything I'm rebuilding.

[Donwill]

Nut Screws Washer and Bolts, first heard when I started my apprenticeship in 1954. Don

[ARWadsworth]

Interesting site. Thank you.

Adam

[Dave]

rubbish and wrong.

Dave

[PeterC]

In what ways, please? I've bookmarked it (didn't read it), so I'll delete it if it is poor.

[Dave Plowman (News)]

If Dave Baker says it's ok, that's good enough for me.

Of course there will be regional variations - and trade ones too - on names for things, but because an Orcadian chippy calls a bolt a screw doesn't make it so. ;-)

[Dave]

A threaded fastener that is intended to screw into a threaded receptacle is defined as a screw if it the shank is threaded all the way up to the head. The head can be any shape. Countersink, hexagonal, square or round like an Allen cap head all fit the bill. As does an Allen grub screw. You never hear about Allen grub bolts.

Likewise a bolt will have part of the shank plain and unthreaded.

A screw is intended to hold two parts together that are not under shear, as the thinness of the threads and the corresponding sloppy fit (threads are smaller that the shank of a bolt, would make it too week to cope with the shear load.

A bolt holds things together and can cope with shear and tensile load because it is thicker along the plain shank. None of the thread should pass through either part to be held together for this reason.

When selecting a bolt, the plain shank should be just long enough to pass through both parts and a washer under the nut will mask off the tapered portion as the thread stops as it turns into plain shank.

The use of a washer under either the bolt/screw head, or nut depends on how it is tightened. If the nut is tightened to the bolt, then it is advisable that a washer is used under the nut. If the bolt is tightened to the nut, then 2 courses of action can happen.

The bolt can have a washer under the head, or the bolt can have a built in washer machined into it.

I have tried to explain this terminology, but I expect others to disagree with me. As I have said before, screws and bolts have become mixed up by differing trades. I was trained by GB's largest engineering company, some time after my apprenticeship ended.

To a chippy, a screw can be either parallel or tapered and threaded to the head, or not. This does not come into this argument.

Dave

[Thomas Prufer]

Here's another one:

Thomas Prufer

[Dave Plowman (News)]

;-) Why do they all come from Tooting?

[PeterC]

Thanks Dave. I'd never bothered to find out the difference between scres and bolts but had intuitively avoided threads in shear unless there was no reasonable alternative.

[Tony Bryer]

Perfectly sensible approach, though Steel Construction Institute's current advice on [larger] construction steelwork connections is to specify M20 x 70mm screws everywhere (unless too short) rather than a whole mix of lengths. The shear calculation is of course on the reduced threaded cross section

[Dave]

in German.

Dave

[geoff]

Pass auf - germans take their jokes seriously

That brings back memories - I have a sheet of paper I picked up from an exhibition with most of those on ... more than 25 years ago

[Thomas Prufer]

Yeah. Whenever they get posted to a german group, there's groans of "not again", so I foisted them off on you.

(Though someone pointed out that some of them actually do exist as standard parts -- I forgot which...)

Thomas Prufer

[Alang]

DIN877 is one. I used to get screws very similar with a transformer for plate mounting