Review on 🧢 BSX Gear BC5B-BK Welding Beanie: Perfect Fit and Protection in Black by Tony Addis

What size is "one size fits all"? I measured mine. My head is 24 inches in diameter at the cap line. It fits me with an elastic band. The elastic band stretches 1 inch. So for hat sizes, 23" is 7 3/8 and 24 1/4" is 7 3/4. I think that fits best if you're in that space. Of course, you could sew on a little more stretch, but the hat will likely look a bit baggy. And when you exceed 24 1/4 inches in diameter, the cap starts to tighten. UPDATE January 27, 2015 - I washed this hat and it has shrunk a bit. It is now firmly seated on the 7 3/4 head.