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Thread: Oil Screws on Mounts?

  1. #11
    You have to follow the bolt manufacturer's recommendations, because some bolts are meant to be tightened up dry (like a wheel lug nut), and some lubricated ( like in a steel truss). There is no rule of thumb.

    You are correct, 10-ring, in that lubrication lowers the thread friction, which means that less wrench torque is required to overcome it, and more of it goes to overcome washer friction and head pressure clamping force. If you want the same bolt preload, you would lower the torque by some percentage for a light oil, and more for a moly grease ( like on a steel truss bracket ). For a bolt into the cast iron block of Diesel engine, you would always use a certain specified thread lubricant. For stainless bolts in an aluminum hub of a fighter plane, no lubricant whatsoever.

    But the bolts on scope mounts are small and don't need to be torqued for preload, so much as to remain in place under shear forces of recoil. Because oil will lower the thread friction so much, I have found that it is best to tighten the screws by feel, which usually comes out a bit higher. If the manufacturer specified a torque for a screw with very light oil, use that - no more an no less. The reason I use a very tiny amount of light oil is because I don't want vibration to loosen the screw. I only put the oil on the first half of the threads, and wipe off any excess. I don't want it squishing out on the head. This is a big advantage when you need to break the screw loose. Even with a lubricated thread or dry fine threads with no corrosion, the breaking torque can run 2.5 times the fastening torque. On a small screw with the wrong sealant or some corrosion, it could be 5x or more, enough to shear off the screw.

    I am no expert, but I used to own a company which sold torque wrenches up to 600 ft lbs, to all the NATO military, particularly aircraft and commercial airliners, as well as building steel buildings to 30 stories. I just remember a few things I picked up, No. 1 being to always check with the manufacturer.

    PS: Loctite and others thread sealers act as a lubricant while you are tightening the screw, reducing thread friction and increasing preload on the bolt. So don't use the wrong Loctite or too much torque!

    However you prepare the threads, it is wise to always use a penetrating oil prior to breaking them free.
    Last edited by Southern; 26-08-2015 at 15:00. Reason: Loctite.

  2. #12
    I always use a small wrap of Ptf tape on my rifles and never had them come loose my rifle has heavy use daily and its on a 270 hope this is something different to use and will never lock it so you will be able to remove them

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