SPRING 2025

14THE DISTRIBUTOR’S

14THE DISTRIBUTOR’S LINKBruno MarbacherDear Reader -with this article I conclude the seriesof articles about thread locking fasteners. I coveredthe essential locking methods and locking elements.There may be additional locking methods and/or lockingelements available. I will write about them when Ibecome aware of them.Bruno Marbacher earned his mechanical engineering degree in Switzerland, he also holds a businessdegree. He started out as a tool and die maker (poly-mechanic) and over the years he has heldvarious management positions in quality and engineering. During his time in America he hasdeveloped and given numerous seminars on topics related to the proper use of mechanical fastenersand machine elements, and assists engineers in solving fastening/assembly issues. His has groomedand directed many young engineers in fastening/assembly technology. He now offers his 40 years ofexperience through writing and lecturing.VISUAL LOCKING ELEMENTS ANDLOCKNUTS FOR SHAFTSSafety Plates With Flaps And TabsLocking plates for screws and nuts have limitedlocking-ability.The locking plates are made from relatively soft andthin sheet metal parts with a clearance hole for the screw.The locking plate is either put under the hex cap screwhead and or underneath a hex nut. After installation ofthe fasteners, a portion of the locking plate is bentupward against one of the six flats. The tab is either bentover the edge or into the corner of a clamped part. Thus,the screw/nut is restricted from turning loose.They only work on fasteners that have corners andflats (Hex cap screws and hex nuts etc.)Locking plates are available for the fastener sizesM3-M52. They are covered by national standards only.Their Locking effectiveness is uncertain. (visual lockingelement).Even for M52 fasteners the sheet metal thickness isonly about 1.5 mm-2mm. If the washers were thicker,one would not be able to bend them firmly against theflats.The sheet metal is too thin to prevent loosening. Thebent washer portion would be pushed away.TECHNICAL ARTICLEUsually when the screws come loose the sheet metalis only partially pushed away and then stops. However,the preload has already dropped considerably.The proper use of a “locking plate” is not to lock screwsand/or nut from coming loose, but to use them as visuallocking elements. Once the sheet metal is pushed awayone can see that the screws/nuts have come loose.There are several different locking plates available forvarious applications:A locking plate with external tab requires a drilledhole in the clamped component. The tab is engaged intothe drilled hole next to a screw head and/or nut. Then, aportion of the plate is bent against of the flats of eithera hex cap screw or hex nut.Locking plate with two flaps requires clampedcomponent to have edges or angles. The longer flap isbent tightly over an edge, the second flap is bent tightlyover one of the hex flats.Safety Locking WiresLocking wires, also known as safety wire, wheninstalled correctly, are an excellent locking method,which prevents fastener loosening due to vibration.CONTINUED ON PAGE 88