It has adjustable D-ring fastening plus a quick-release buckle. Size-wise it fits my head so around 59-60cm, that would likely be sold as L or possibly even XL. The foam pads inside can be tailored to alter the fit slightly - there's a permanent thick foam lining with thinner foam/velcro pads for customising the fit; I'm sure you could find more thin ones to adjust the fit further, but none are included in this sale.
eBay