The only three lead crystals I have seen have one lead connected to the
crystal case (it is obvious on the ones I have seen), and that lead is
intended for mounting and grounding.  It is not connected to anything
inside the case.  Hope yours are like this!

Nick Taylor wrote:

> Another xtal question:  a few days ago I ordered a few crystals,
> 7.3728MHz, 30pF, HC49/U case.  They arrived yesterday, and much
> to my surprise they each have three leads!  I've never seen a
> three wire xtal before.  As yet I've not had a chance to experiment
> with them ... does anyone know anything about three wire xtals?
> Should the center lead be grounded like a ceramic resonator?
>
> Thanks,
>  - Nick -