Specialized--Snell certified. 24" should be covered with a large in most. Not all models will fit exactly the same within a brand. Luckiily I've found the Specialized lids I've bought fit my round-oval head better than others, with my current lid fitting best in terms of shape. It's important to get the smallest size that fits properly which means not settling for a square shaped bucket in a larger size to fit a round shaped peg.