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Re: Lag Bolts

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On May 4, 2006, at 10:47 PM, S. Gordin wrote:

a) "carriage" and "coach" screws are the same type of hardware.
b) "coach screw" is a more British term.
b) "coach" and "lag" screws terms can be used interchangeably.
That's a little different usage, probably industry specific. What I've always heard termed 'carriage bolts' are now (ANSI B.18.5) are 'Round Head Square Neck Bolts.' The 'square' portion is just under the head to create interference when they're tightened down so they can be tightened without holding the head. Variations are 'Round Head Finned Neck Bolts,' and 'Round Head Ribbed Neck Bolts.'

Lag screws are wood screws with a coarse thread. According to ANSI B18.2.1 they come with.

There's also a distinction between bolts and screws: bolts are tightened with a nut. Screws don't use nuts and either form their own threads or engage female threads formed in the part to be joined. That's another distinction between carriage bolts and lag screws. None of the fasteners shown in 'Machinery's Handbook,' which is a standard reference for such things, makes any distinction is the section on British standard fasteners.

I suspect that in practice, these terms are very loosely used, both by engineers and craftspeople, and you shouldn't assume that any usage you run into is necessarliy precise. I also wouldn't waste a lot of my time arguing with people and trying to score points about the distinction between screws and bolts and lag screws and carriage bolts and whether or not one definition is more correct, until there are contract issues at stake.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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