EGR Bolt (Exhaust Manifold Side)

Can someone tell me with certainty what size the head is on the EGR bolt on the exhaust manifold? I am pulling the manifolds on my RMW and that one bolt is the only thing keeping the PS one from coming out of the engine bay.

Access to the bolt just plain sucks, as I am sure you know. I got a 13mm wrench on it today and it seemed to fit (a 1/2 seemed not to fit) but when I started putting some torque into it it felt like the wrench was slipping. I don't want to round this thing. The combination of SAE and metric on these cars is bizarre so anything I am pulling something for the first time I question wrench and socket fitment.

Any tips for the angle of approach on this thing, while we are here? Getting the pipe back on and bolted up when I reinstall the manifold will probably suck as much as getting it off.

In case some other shlub finds himself in this position, here is what I found:

Dropping the downpipe and cat gives you much better access to the EGR bolt. It's still tight, but I was able to determine that the head is 1/2 inch. Thankfully mine was not all rusted to heck and broke loose with moderate torque.

It would help if you referenced exactly what you are working on since your vehicle is not listed in your sig.

Olds Weighty Eight wrote:

It would help if you referenced exactly what you are working on since your vehicle is not listed in your sig.

That's a good point.  The car is visible in my avatar, but a specific statement about it would be best.

It's a '95 RMW.