Metric Hardware - The Basics


Ultimate Garage used to offer a broad selection of high quality metric hardware to DYI enthusiasts and restoration specialists. I will be selling off some excess inventory, keeping a nice assortment for myself in the event I ever retire and find myself wrench on cars (for fun). The comments below were written in the mid to late 90's.

The Marketplace - I've spent many years evaluating 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") is of decent finish and must meet the stamped (8.8, 10.9, etc) standards. However, I object to the relabeling and to paying premium prices for hardware, tools and other products imported from China or Taiwan.


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, Porsche & Mercedes have 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 the 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 used by many manufacturers 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 chromate 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.

Some 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 gauge (3.5-4/10,000" 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 must 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). All of our treated hardware is accompanied with a Letter of Certification from the plating company assuring us (and our customers) that the hardware meets the stated specifications.

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. The Ultimate Garage now stocks over one million fasteners, from sizes 3mm through 16mm (other sizes available via special order). Please refer to our Metric Hardware Price Sheet for details on specific items.