Bolt (cap screw) question

[theoldwizard1]

Why do some bolts have threads all the way up to the hex and some don't ?

 

[driver]

The industry standard thread length is 2 diameters plus 1/4". We did get some special bolts for work that were 3" long and fully threaded but they weren't off the shelf.

 

[red92s]

Fully threaded bolts in longer lengths are commonly referred to as "tap bolts".

 

[zkling]

Combined shear and tensile loads vs tensile only loads. As well as minimum clamping thickness range.

 

[Seagoon]

AFAIK bolts(Those with a plain shank between head and thread) are intended for use with a nut while machine screws(Those with a thread all the way to the head) are intended for use in a threaded hole.
They can have different head types - hex,cap,slotted etc.
HTH

 

[kazlx]

That and you typically don't need to engage threads all the way up to the head on longer bolts. You aren't going to use a 6" bolt and run a nut to hold two pieces of sheet metal together.

 

[kbs2244]

If you think about it threads will weaken a shaft.

 

[Dave455]

In British terminology, a fastener threaded all the way is a screw, not a bolt! I believe this is the correct term in the U.S. too, which my elderly Machinerys Handbook confirms!

Using British terminology again, a screw with a hex head is a 'set screw', but I know U.S. terminology differs here!

 

[F124C]

^^^ x2

Al.

 

[zkling]

Actually IIRC the technical definition between a screw and a bolt is in how they are used. A bolt uses a nut to act as the compression agent where as a screw uses a tapped hole in a mating part for compression.

So one could say all bolts can be screws, but not all screws can be bolts.

This is independent of what the OP is asking though IMHO.

 

[steel 35]

If you think about it threads will weaken a shaft.

In some situations.