Toolbox length

Hey guys. Sorry to ask but I'm away from my truck for a bit and don't want to just measure a random stranger's bed. I'm looking at buying a crossover toolbox and have googled and searched TW to find a definitive answer and haven't come up with anything.
What is the max length for a crossover so it doesn't sit over the sides of the bed? I'm looking at this weatherguard: https://www.weatherguard.com/truck_tool_boxes/view_products.php?subcat_id=9 , and the top is 66". I found someone that said they had it in their truck but (attempting to envision in my head), I'd think 66" is too wide. If the bed is 57.5 that would mean the sides of the bed would have to be at least 5 inches each for this box to fit. In my head they don't seem like they are. I'm picturing 3"-4". Is anyone up to throwing down a measuring tape real quick for me?

 

Saw that thread in my searches, but no. Looking for one that sits the way you see 99.9% of toolboxes sit (on top of the rails). Just need to know how wide the bed is from the outside of the side rail across to the outside of the other.

The distance between the two arrow points

 

Here you go. Now you don't have to picture it in your head. This is my Weatherguard that is 66 inches. Fits nice.

 

And that 66" matches this picture I took as a reference for another thread. I was measuring from the outside edge of the black rail cap. 66" would give you about 1/2" of the lid past the caps on each side. Looks like a good fit to me.

 

Awesome!!! Thanks guys. That is definitely the one I'm getting then.