Boonie Hat Size Adjuster

I was gifted a Boonie hat - this particular one seems to be of a very common design. It said “one size fits all” - but I'm not all, so it was way too big for me. 

There's a band around the hat - but no way to adjust it. So I designed this little thingy where the band can wrap around to make the hat smaller. 

There are multiple pins for different sizes. My head circumference is 56 cm and I use one of the center pins - so there is room for larger and smaller heads 😁