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    Re: Sextant repair
    From: Lu Abel
    Date: 2006 Mar 20, 21:22 -0800

    You should await a reply from a expert on metric screws, but your
    measurements fit a 2-56 screw very well.  Outside diameter of a numbered
    screw is 0.065 inches plus 0.013 times the number, which works out to
    0.091 inches for a 2-56 screw.   Actual screw are often a few
    thousandths undersized, which fits your measured diameter of 0.089 very
    It's not clear from your note whether the screw or tapped hole is
    damaged.  Suggest taking the undamaged piece and trying to mate it with
    an appropriate 2-56 part (you description sounds a bit more like the
    tapped hole is damaged, so why not try gently threading a 2-56 nut on
    the screw?).
    Lu Abel
    Philip Lange wrote:
    > To the list.
    > I have a not so old, 1968 ,  C.Plath sextant that I am trying to
    > restore. The thread that secures  the pivot arm to the frame is buggered
    > and needs a to be chased. Trouble is I can not determine  the proper
    > thread. The screw measures .089 +- (2.26 mm) in dia and I have counted
    > and calculated 56 tpi. (Measured by a caliper not a mike. Could be a
    > little off.)  The closest I can find is a #2 56, but I doubt this as it
    > is of German manufacture and I suspect the thread is metric. I would buy
    > a tap if I knew the right thread.
    > Watch and clock makers are not to be found in this neighborhood.
    > I know this is off the wall, but, can any one help me ?
    > Thanks
    > Philip
    > * Philip & Marilyn Lange
    >    AE4OV & KD4JRC,
    > *  S/V ORYOKI
    > *Witness 35 Catamaran
    >  http://www.oryoki.net
    > **
    > *

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