Numerous responses have suggested nut-sert type fasteners with machine
screws for applications in sheet metal, which is what you're attempting.
They're what the automotive and commercial equipment manufacturers use
because attaching parts to sheet metal isn't as simple as using a screw.

The majority of steel fasteners aren't intended to COLD FORM tight (binding)
threads in steel, which is the part that you seem to be ignoring. Steel
isn't like wood, and sheet steel has more limitations.

If the screw is hard, it will snap.. if it's mild steel, the threads will
smear.. no worky.
There are self-drilling screws that work well with thin steel, but may not
work well (100% of times tried) for everyone.

With many of the fasteners you're hoping will work, you end up with a small
portion of one thread (10-30% of a single thread) holding a load. You'd get
better contact with a nail, as in woodworking, but not appropriate for
metal.

You're most likely either going to need threads in the base material
(nut-sert), or screws that can CUT threads.. self-tapping screws, also
suggested in earlier responses. Trouble is, there isn't much thickness for a
reliable connection.

Self-tapping screws are intended to be installed with a specific (ideally
punched) hole size, which isn't easily made with a hand drill.. the 3-sided
hole in thin metal, everyone's seen that, right? Or the DIY-types that work
the drill around in a large orbit as a matter of habit.

http://www.theindustrialdepot.com/ri...llow-zinc.html

http://www.youtube.com/watch?v=Wf-mwytdurQ

A gurl (with dimples) can do it

http://www.youtube.com/watch?v=p8oMHuLxCcs&NR=1

Installing the rivnut/nut-sert type fasteners doesn't actually require
special tools.. a stud, washer, nut and wrench will usually suffice. There
are styles with ribs to grip the sheetmetal hole to prevent the fastener
from spinning while installing them.

http://www.rivetdirect.com/

An alternate fastener might be a drive rivet, which provides all of the
fastener's diameter for shear strength (unlike hollow pop-type rivets).

http://www.rivetdirect.com/driverivets.html


Machine screws/bolts with a very short shoulder on them (not threaded all
the way to the underside of the head) will have a greater shear strength,
used with the above rivet-nut inserts.
The nut-sert-type fasteners are a solution, not something that needs to be
analyzed.

The ultimately cheap, reliable solution will be MIG wire, properly applied
with a welder.

BTW, threads on most fasteners are rolled (displaced), not cut.

--
WB
..........


"Existential Angst" wrote in message
...
Awl --

I think the whole sheetmetal/drywall screw thing is resolved with the
"deep thread" class of screws:
http://www.gardensheds.greenhouses.a...ew-threads.htm
http://www.theindustrialdepot.com/de...ead-screw.html

For example, a coarse sheetrock screw measures .094/.146 minor/major diam
The drill-point sheetmetal screw (that I wound up using) measures
.130/.165.

So the SR screw, being a deep thread, has *a lot* more bite.

McNeely's has a variety of deep thread screws. One section is he
http://www.mcfeelys.com/search/fsl , altho it's not clear just how deep
is deep.
In http://www.mcfeelys.com/tech/dimensions.htm , it's not clear if "B"
(their body diam) is the same as the root diam.
If so, this is not as deep a thread as the name suggests.
McNeely's deep-threads (inch length) are about $20/1,000 -- McNeely's
seems pretty reasonable.


But here's the Q:

Can I get REALLY deep thread screws? What would they be called, or their
application classification?
I'm thinking on the order of .125/.200, ie, about .040 grabbing on the
radius.

I've hunted around, but haven't come across anything deeper than the reg.
deep thread spec.

Any ideas of what a custom run of screws might cost? Quan, $$ ?

I'm thinking if I ordered a standard #12 or #14 screw, and asked them just
to set the machine to cut a little deeper, I'd get the screw I wanted....


Iny ideas on who might do this?

--

EA