On 20/01/2016 15:36, Adrian wrote:
On Wed, 20 Jan 2016 13:32:02 +0000, newshound wrote:

Probably a daft question but is one finish better than another? Ebay
sellers seem to have black ones or zinc plated yellow ones. Is one
finish more durable, less likely to rust than the other?

Black are most common in things that I have dismantled. You sometimes
see traces of rust at the piercing, the black finish seems reasonably
corrosion resistant. I wouldn't use them in the bilges of a boat, but
they seem to be OK in stuff that lives outdoors.

They're used on 2cvs for the body-chassis bolts - black finish, usually.
As such, the threaded portion is exposed on the underside of the car, and
they can be really quite horrific looking. It's usually about 50% that
have to be cut off, if the car's never been apart - but that's after
decades of use.

I guess they rely on mud and corrosion to glue the body to the chassis,
preventing the vibration which would otherwise shake them loose! Or the
corrosion on the protruding bolt, I suppose.

:-)