On Sun, 13 Jun 2010 15:36:11 -0500, spaco wrote:
Existential Angst wrote: snip
Can I get REALLY deep thread screws? What would they be called, or
their application classification?

Answer: weak.

Spax screws are fairly strong. They look like sheet metal screws
with wide threads [but are intended for wood (eg "unpiloted hard
maple") rather than metal]. In following picture, note serrations
on first three turns, to cut mating thread.
http://www.highlandwoodworking.com/spaxpan-headzincplatedscrews10x341.aspx

In OP's application, if the space beyond the steel jamb is hollow,
anchors like following might work.
http://www.alestech.com/molly-jacknut-anchors-4sjnws-item_13152.html

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jiw