I am slowly putting together my 1972
Duster 340. As I assemble the front end,
I have noticed that a lot of the bolts look
like giant self-tapping screws. Do they
actually cut threads? Some of the holes
they go into look like very thick metal, like
the big K crossmember to the frame, the
steering gear to that crossmember, and
so on. I don’t have a problem with any of
these, I am just curious.
That’s a great question with an interesting
answer. That “thick metal” most of
them screw into are actually welded-on
nuts and are fully threaded. Those “self tapping”
screws you refer to feature
what is actually what is called paint cutter
threads. Many of them have also an
extended dog-nose-looking snout, which
is called pilot point. The two features are
often combined into one screw, so the
assembly line worker could simply air-tool
them in with little chance of problems
such as stripping, cross-threading, etc.
Long, long ago, when I was a kid, we
called this effect cross-grossing.
