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Hardware & Fasteners-The Basics

         I've spent the last few months looking at the supply of metric
hardware and fasteners available to the consumer market for automotive
application.  Most of what's out there is adequate at best with quality
taking a back seat to low price (this low pricing is generally not passed on
to the end user).  In fact, in speaking with the local Wurth sales manager
(Wurth USA is located right here in Northern NJ), very little of the Wurth
products (chemicals and hardware) are still made in Germany.  This
contradicts many of the claims made in the various automotive mail order
catalogs (Griot, Imparts, Eurasian, etc) that they carry only quality
"German" Wurth hardware.  Wurth does have better standards than most and the
Taiwanese and Italian hardware they distribute (often packed in bags labeled
"Made in Germany") has a decent finish and must meet the stamped (8.8, 10.9,
etc) grade specifications.  However, I object to the relabeling and to
paying Wurth's premium prices and just as BMW dealers forced me into the BMW
parts business and Snap-on drove me into the tool business, Wurth has driven
me into the metric hardware arena.
Grade & Origin - You can tell a lot about a fastener just by looking at it.
On most bolts, you'll find the name or initials of the manufacturer on the
head of the bolt.  This will lead you to the country of origin.  BMW has
typically used hardware by Kamax, Verbus, Ribe, Lobo, etc of Germany.  They
are now sourcing a fair amount from Agratti of Italy (initials OAV).  Much
of what Wurth is selling is by "JH" of Taiwan and "OAV" of Italy. I'm told
by many of the larger metric importers to be careful with some of the
fasteners coming out of Brazil and Eastern Europe (the quality and finish is
often poor). Also on the head of the bolts (and on many of the nuts as well)
is the grade (tensile strength)...metric grade 8.8 is standard automotive
grade with a tensile strength of approx 120,000psi.  The next common grade
is 10.9  (9.9 is available but not very common) which carries an average
tensile strength of 150,000psi... this grade is recommended for most
drivetrain, cylinder head, suspension and brake applications. These bolts
are typically "black only" although they can be obtained with a yellow zinc
dichromate finish (more on that later).  There is also available a grade
12.9 (176,000psi tensile strength).  This is the grade BMW uses for flywheel
and connecting rod bolts.  These bolts are generally available as socket
head (allen type) and come in a black finish. On nuts, you'll generally see
the grade stamped as just "8", "10" or "12".  Washers (split and flat
washers) are not rated.
Materials & Finish - the common automotive fasteners are zinc plated steel
(silver), yellow zinc dichromate plated steel (yellow or reddish/orange
finish), and heated treated steel (black). Stainless steel is used for
rust/corrosion resistance and available in a 304 (A2) or 316 (A4)
construction. The 316 is a marine grade and is totally non-magnetic.
Stainless steel does not have as high a tensile strength as regular steel.
Use a property class 70 or higher for automotive application.  The most
common fasteners on German cars are the yellow zinc nuts/bolts and
washers...however, most dealerships, independents and parts houses only sell
the plain ("silver") zinc because of availability and price (Note: all
fasteners purchased directly through BMW via part number will come as black
or yellow zinc).  Most of the yellow zinc hardware that I stock is plated
locally to my specifications. The hardware is purchased in bulk from select
manufacturers as black heat treated hardware. It is tumbled cleaned and acid
etched ("pickled"). The hardware is then plated to spec (4/10,000" thickness
vs commercial standard of 2/10,000") and chromated to spec (yellow zinc
finish).  The final step is very critical (and often skipped by many of the
low-end manufacturers)...the hardware should be baked to release the
hydrogen from the plating process ("hydrogen embrittlement") or you'll
severely compromise the tensile strength of the fastener (8hr baking is
specified vs commercial standard of 1-2hrs).  The next time a hardware
salesman or parts house tries to defend the quality of their fasteners and
says "they're made to our high standards", ask him what those specifications
are.
I'll try to post a follow up segment on this subject covering types of
fasteners (DIN spec) and sizes that car enthusiasts/professional mechanics
should stock in their home garage or shop.  Please feel free to contact me
directly if you have any questions or would like a price sheet of the
fasteners that I distribute (send e-mail with mailing address).  SD

Steve D'Gerolamo c/o The Ultimate Garage,  Emerson, NJ  (201-262-0412)