Freeze plugs

[RedArrow]

Hi everyone. On a `81 n/a d24 engine there was a vw block heater in 4th hole (manifolds` side) that has been removed, i think.

Where to find the proper freeze plugs for the d24 and d24t engines?
(Are they using the same part? same size?)

I will measure the diameter, but;
one more thing (if you have/had one out): How thick are they? Please confirm about the sizes.