It's a 17mm Allen.

I bought a regular "L" shaped Allen wrench and cut a short piece off.  I
insert that short piece into the plug and turn it with a gear wrench.
To me, it works much better than the Allen "Sockets" sold for this purpose.

Mike

Jeff Clayman wrote:
> Hi,
>
> I have a female type nut in my differential fill hole for my 87 a/t 2.1.  Anybody know what the wrench to get this out is called?  Part #?
>
> Jeff
>