6-sided ...wrench?

[Mac53]

Hey all!
Been a while since I posted, but my friend sent me a picture of a tool that has me stumped.
Gas? Wagon? Does anyone have an idea?

[Chillylulu]

Multi purpose fill box star wrench
http://oiltradessupplycorp.com/product/multi-purpose-fill-box-star-wrench-flat-cast-iron-new/

$30.00 new

Chilly   

[Mac53]

Thanks, Chilly!
So, it is just used to open fill boxes for...fuel oil? That explains why we have never seen one... we don't have a lot of that down here, mostly just heat pumps.