In Japan, the main way to prevent thread loosening is to use pre-assembled screw sets, where the screw is purchased with a straight or spring lock washer already placed on the shank of the screw. This helps prevent washer loss and increases efficiency by reducing assembly time. Due to the wide variety of possible combinations of screw and washer, pre-assembled screw sets can cover almost any imaginable fastener situation.
And ranging from flat washers to spring lock washers, from small Phillips head screws to hexagon bolts and hex socket bolts, the choices are practically endless. Additionally, the choices of materials and plating are also wide, from steel and stainless steel, to brass materials, and plating with trivalent chromium in trivalent zinc white cr3+, nickel as well as other treatments. And of course, the screw shank thicknesses and screw shank lengths are also unique to each different application.