SUMMER 2026

12 THE DISTRIBUTOR’S

12 THE DISTRIBUTOR’S LINK Guy Avellon Guy Avellon has been in MRO and Fastener Distribution for over 30 years, in such positions Sales Engineer, Chief Engineer, Manager of Product Marketing, Product Engineering & Quality and Director of Quality & Engineering. He founded GT Technical Consultants where he performs failure analysis, lectures on fastener safety, works for law firms and designs/audits Quality systems. He is a member of SAE, is Vice Chairman of the ASTM F16 Fastener Committee, Chairman of the F16.01 Test Methods Committee and received the ASTM Award of Merit in 2005. Guy can be contacted at 847-477-5057, Email: ExpertBoltGuy@gmail.com or visit www.BoltFailure.com. WHAT FASTENER DISTRIBUTORS NEED TO KNOW ABOUT METRIC THREADS The DIN (Deutsches Institut fur Normung) standards have been modified to follow ISO (International Organization for Standards) recommendations. The United States coordinates their efforts with ISO through ANSI, the American National Standards Institute, although there are still some slight differences between standards. Fastener Designation First, when ordering or identifying the dimensions of a metric fastener, all metric fasteners are preceded by the capitalized letter ‘M’, which also designates a metric thread form as being standard. Then, similar to how inch series fasteners are identified, the diameter is listed with the thread pitch, length, Property Class and product description. For example: M12 x 1.0 x 50, 10.9 Hex Cap Screw This tells us the diameter is 12mm, the thread pitch is 1.0mm and the length is 50mm. The property class is a 10.9 and the product is a hex head cap screw. Further information may indicate coating type or any other supplemental treatment. Thread Pitch Users must be aware that there are three types of thread pitches available: the Standard thread, which is similar to the UNC; the Fine thread, similar to the UNF; and the Japanese thread which is between the two pitches but is used only on the M10 and M12 fasteners. For example; an M10 fastener can have a thread pitch of 1.0mm, 1.25mm and 1.50mm and the M12 may have a thread pitch of 1.25mm, 1.5mm and 1.75mm. CONTRIBUTOR ARTICLE Identification is extremely important because many metric sizes are very close to the inch series. The nut or fastener may start to become engaged but additional tightening could result in thread stripping or seizing. For example, a ¼”-28 fastener has a diameter of 0.250” compared with an M6 which measures 0.236”. The difference is 0.014”. The thread pitch on the M6 is 1.0, which is roughly equivalent to 25.6 threads-per-inch vs. the 28 TPI for the inch fastener. These examples present a very close difference; visual confusion is easy; detection impossible and the threads are easy to strip. The resultant assembly of mixing inch and metric products will produce clamp loads from 25 to 60% less than expected, providing the threads haven’t stripped or have begun to strip when tightening, in which case the loads will be close to 100% lost. The following table will illustrate other examples of potential clamp load losses when mixing metric and inch fastener components together. Inch Threads Vs. Metric Threads Inch Bolts Metric Nuts 10-32 M5 x 0.8 1/4”-28 M7 x 1.0 5/16”-18 M8 x 1.0 3/8”-16 M10 x 1.5 7/16”-14 M12 x 1.75 1/2”-13 M14 x 2 3/4”-10 M20 x 2.5 3/4”-16 M20 x 1.5 CONTINUED ON PAGE 90