This head guard is fully adjustable at the back with several velcro straps (hook and loop design) which makes it suitable for most adult heads. To get a snug fit simply pull at the Velcro straps and attach as required for a comfortable fit. We are confident that you will be pleased with this product and if it does not meet your expectations then we are happy to exchange or refund. The product is made to the highest specification and is quality tested and guaranteed. This has made it the choice of professionals and that is the reason we are supplying these to world class health clubs, gyms and Boxing clubs.