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Philip:

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
well.

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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