Years ago where I worked we began using Bowman fasteners exclusively and soon after they supplied us all mechanics were treated with a 2 hour taped seminar on nuts and bolts and I thought, "How boring, I already know everything I need." We went to the seminars 6 at a time and when I heard some who had attended before me how in the seminar it was stated split washers (lock washers) were useless I attended with skepticism and I knew lock washers were necessary because how smart I was. I want to tell you that was one of the most interesting and enlightening 2 hours I ever spent. Who would have thought? This was before imports came commonplace and communist bolts, I mean metric bolts, came into prominence so it was focused on English sized bolts but the facts are true in metric. I learned about hardness and grade markings. I learned about how the stretch in a bolt keeps it tight and how the even the slightest bit of lubrication can affect the pressure exerted by a bolt. I learned that a hard bolt may be the worse one to use in arctic climates and, yes, I learned why split washers are unnecessary. Answer: when compressed they become a flat washer and, no, the edges of the split do not dig in to hold the fastener from backing out. Proper torque holds the fastener tight however sometimes a thread lock adhesive is necessary or a locking type nut or bolt which is a subject in itself. Machine screws are another subject and were not addressed in the seminar.
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