WINTER 2025

42THE DISTRIBUTOR’S

42THE DISTRIBUTOR’S LINKBruno MarbacherDear Reader, the main purpose of a thread formingscrew is to form the mating internal thread. By doing soit forms a play-free thread. Thus, preventing wobblingthe same way a locking adhesive does. In this articlewe address the locking effectiveness of thread formingscrews,In addition, we highlight what measures one can taketo prevent joint relaxation and preload loss.Bruno Marbacher earned his mechanical engineering degree in Switzerland, he also holds abusiness degree. He started out as a tool and die maker (poly-mechanic) and over the years hehas held various management positions in quality and engineering. During his time in Americahe has developed and given numerous seminars on topics related to the proper use of mechanicalfasteners and machine elements, and assists engineers in solving fastening/assembly issues. Hishas groomed and directed many young engineers in fastening/assembly technology. He nowoffers his 40 years of experience through writing and lecturing.LOCKING EFFECTIVENESS OF THREAD FORMING SCREW& DESIGN MEASURES TO PREVENT PRELOAD LOSSThread Forming Screws For SecurelyLocking Fastened JointsThe thread friction of thread forming screws typetaptite is extensive. hence, having an excellent vibrationresistance. They also do not unwind or even fall off.The locking effectiveness of taptite screws has beentested in a junker vibration testing machine for aprolonged time. They did not come loose and the taptitescrews ultimately broke due to a fatigue failure.The fact that these screws are very reliable and safe inaddition to eliminating tapping make the screw very costefficient. They should be used instead of regular screwswhenever possible.A zero-clearance intersection distinguishes betweenthread forming screws and thread cutting screws. Sincethread forming screws create threads simply by ‘pushing’into the material, it forms a very tight fit between thematerial and the screw. This zero-clearance fit is perfectfor parts that experience a lot of vibration, such as inindustrial equipment.The self-locking mechanism of a thread formingTECHNICAL ARTICLEscrew means that that locking elements are no longernecessary. Thread forming screws, by their very principle,produce a very tight fit, a certain amount of radial stressis induced that will take a lot of effort to loosen.I do not know whether other thread locking screwshave been tested in the junker testing machine and howthey performed. A thread forming with low driving is idealfor many applications, but some types produce a lowerradial stress and therefore locking ability may be lower.Powerlok ScrewsPowerlok provides locking ability through thecombination of a 60° - 30° thread form and a trilobularthreaded section. The major diameter of the screw islarger than the major diameter of mating internal thread,thus the thread crest presses itself into the thread root ofthe mating thread.CONTINUED ON PAGE 108