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Rob Is absolutely correct! This has come up before (fine vs coarse threads
in Al.) and all I can tell you guys and gals is: coarse threads in aluminum
and coarse OR fine threads in steel. Don't think you can fool Mother Nature
by screwing in a Heli-Coil (or equivalent) as the insert is installed in
fine threads. Look it up for yourselves - fine threads in Al will not react
the high loads imposed by the bottoming out hydro cylinder.

Take a look at all the tapped holes in your Lycoming (or Continental too,
though I'm not as familiar with the Cont.) and where there is any load,
they're all coarse.

Dan Schaefer

LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.