What size is the fork top nut on 40mm forks?

What is the nut size on the top of the fork tubes of a 40mm fork? The nut/plug that sits on top of the top triple tree. It seems larger than 36mm but I don't have a socket larger than that to try on it.

It measures 1.460" or 37mm.

Thanks, Ron!

Hmmmm........nobody seems to sell a 37mm socket. What gives?

I found a 37mm six point socket made by Ozat, p/n 16M37, which fits the fork tube top nuts. It's a socket which focuses the power on the shoulders of the nut and not the corners (which these nuts don't have). It worked great!