Returned your PM, but i will post it here incase anyone wants to check there own, Knowing nissan they could all be different.
I havent checked mine but i assume they are 3" sports bars on the D40.
The easiest way to find out the exact diameter is measure the circumference of the bar, than use circumference divided by 3.14, that will be the diameter of bar.
I have the original from the truck and when I was looking to find another to get the mounts I was given another 2 sets .
I actually have a Hilux bar on mine as its way stronger to mount lights n stuff on .I cut the mounts of the Navara bar and bolted them to the tubes of the Hilux bar
Ok how about
I have a modded sports bar on mine that was mistakenly bolted onto a different truck so I made it fit for purpose and bolted it on mine.
lol