On Sun, 7 Dec 2008 13:18:55 +0100, "Steve Lusardi"
wrote:

Karl,
Saving the threads, even if it were possible is a waste of time, because the
treads have become aluminum oxide and have no residual strength anyway. Next
time use anti-sieze at assembly. Most likely the fault was electrolysis, as
they were probably diecast and zinc is often alloyed with the aluminum to
promote flow in the mold. In the presence of water, the unit becomes
thousands of little batteries.

Is there something unique about diecasting alloys that make them prone
to becoming "thousands of little batteries?" Leaded red brass
(85-5-5-5; copper-tin-lead-zinc) is very durable in sea water, and is
composed of metals much more widely separated on the galvanic series
than aluminum and zinc, which are quite close to one another.

--
Ned Simmons