Helicoils and T-Serts

["Smith, Kirby A" <kirby.a.smith@lmco.com>]

A coupla' decades ago, when I was more closely involved with hardware,
we found helicoils would often back out with the screw, leading to
obvious problems.  An alternative device, known then as a T-Sert, was a
better idea, IMHO.  The T-Sert resembled a through-tapped section of
threaded rod.  The inner thread fit the bolt or screw to be used; the
outer thread matched the tap size used with the oversized hole.  Unlike
the wire form of the Helicoil, the T-Sert had a proper thread form on
interior and exterior.  There were two axial grooves in the outer thread
form.  After the T-Sert was threaded into position, two small pins were
driven down the axial grooves, thereby locking the device into the
tapped material.  

I suspect that Helicoils can be made to work, however.  If a helicoil
was installed with Locktite, and the screw to be used with it
lubricated, the helicoil would not likely back out.  Note that for
exhaust manifold studs, the lubricant has to be NeverSeize, or
equivalent.

         ....  Kirby  (kirby.a.smith@lmco.com)
                   New Hampshire, USA
                      2 X 1988 90q