WINTER 2025

8THE DISTRIBUTOR’S

8THE DISTRIBUTOR’S LINKLaurence ClausLaurence Claus is the President of NNi Training and Consulting, Inc. He has 25 years ofexperience with a medium sized automotive fastener manufacturer, holding positionsincluding Vice President of Engineering, General Manager, Director of Quality, Directorof New Business Development and Applications Engineer. In 2012 he formed NNioffering technical and business training courses as well as technical consulting, expertwitness and consultation work. He can be reached at 847-867-7363 or by email:Lclaus@NNiTraining.com. You can learn more about NNi at www.NNiTraining.com.PREVAILING TORQUE FASTENERSAt 8:37p.m. on the evening of July 13, 1977, alightning strike to a power substation feeding New YorkCity would trigger one of the most epic power outages inmodern history. The first lightning strike would be followedby a second about twenty minutes later that would resultin a cascading procession of equipment shutdowns whichwould deprive much of New York City of power for almosttwenty-five hours. Although no fatalities were credited tothe power outage, massive looting occurred leaving 550policeman injured, 4500 looters arrested, and upwards of0,000,000.00 in damages and losses.In the aftermath of the event, the U.S. Departmentof Energy’s Regulatory Commission Task Force wouldconclude that, “[the root cause of the outage was from]equipment malfunctions preventing the proper automaticrestoration to service of three of the four lines struck, andleading directly to loss of additional transmission circuits,resulting from a loose lock nut on a control rod of a circuitbreaker and a bent contact on a protective relay, both atthe Millwood West Substation.” A couple penny nut wasresponsible for all of this chaos.The word “lock nut” or “locking fastener” is a little bitof a misnomer. It leads one to believe that the use of sucha fastener indefinitely secures the joint in its intended state.In other words, if the joint is designed to provide a specificamount of clamping load, the word “locking” suggests thatthe fastener is able to assure that such the clamp load is notlost. Unfortunately, most “locking” fasteners do not deliversuch desirable performance, but rather only provide somedegree of safety against self-loosening and fastener loss.Self-loosening is a complex problem which experts areTECHNICAL ARTICLEstill trying to fully explain. However, Bickford states that“Everyone agrees that a threaded fastener will not loosenunless the friction forces existing between male and femalethreads are either reduced or eliminated by some externalmechanism acting on the bolt and joint.” Furthermore,self-loosening only occurs if cyclic, transverse loads (likethose subjected by vibration) are present and there is slipbetween the mating threads or the contact surface.There are many fastened joints where preloads are lowor non-existent. The late fastener expert Bengt Blenduffused to refer to these fasteners as “place keepers”. Eventhough these joints are less demanding, he reminded usersthat keeping them intact and in-place was often critical tothe performance of the product they were applied in. Thus,having options to prevent self-loosening is important andhas spawned an entire class of fasteners.These fasteners fall into one of two categories;“locking fasteners” and “prevailing torque fasteners”. Alocking fastener is one that contains a pre-applied adhesiveor mechanical means (such as a drilled hole and cotterpin, mechanical tab washers, or locking wire) to preventthe fastener from moving or retain it in-place. On the otherhand, a Prevailing Torque Fastener is one that providesor generates some form of interference between matingthreads to withstand or prevent disassembly that resultsfrom ordinary vibration. According to the IFI’s Glossary ofFastener Related Terms, Prevailing Torque is the torquerequired to overcome kinetic friction of the mating threads,plus the torque required to overcome the locking featurewhen 100% of the locking feature is engaged and afastener is not seated.CONTINUED ON PAGE 88