Threads -- a practical tip

[Scott Fisher <sefisher@domain.elided>]

Some of you may not know this neat tip for matching threads when buying
new nuts and bolts.  It's especially useful if you are taking apart a
car that has, shall we say, "mixed nuts" on it due to a succession of
patches and paste jobs by previous owners.

If you're trying to match a nut, first find a bolt that fits it.  Make
sure the bolt *really* fits it, too -- spin it more than just the first
few threads into place, as some SAE threads are close enough to similar
metric thread sizes that you can get one or two turns before the thing
seizes up and goes no further (ask me how I know).  But the tip here
only works on bolts, or at least something with external threads.

When you get to the hardware store, find a bolt that looks like it's the
same diameter as the one you've removed from the car.  Then, hold the
two bolts together so that the threads match up like the teeth on a pair
of gears.  If they do -- that is, if the two bolts mesh perfectly --
they're the same size.  If they don't -- if the bolts can't get
parallel, or if the teeth on one clearly skip out of the teeth on the
other -- look for a different bolt, and keep looking till you get two
that fit perfectly.

Note also that new hardware is one of the least expensive niceties you
can do to a car, especially a car you're likely to work on more than
once.  A box of new nuts and bolts (apart from oddball sizes or
specialized hardware, of course) doesn't cost much and makes life *so*
much easier when it comes time to take the car apart again.  I still
remember the time I used cadmium-plated nuts and bolts to hold the
radiator and shroud into my MGB -- surely it was overkill structurally,
but the next time I had to take the engine out (and the shroud comes out
first on that car), none of the bolts had rusted, corroded, or become
stuck.  One good twist to unseat the spring washers and they came off
easily, making the replacement job so much easier. 

And I have to say that the gold-colored hardware looked really
impressive against the BRG paint of that car... :-)

- --Scott Fisher
  Sunnyvale, CA

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