A: The ‘mark’ of your helmet is the model number. The full face, cut away and surf helmet models have not been modified for a number of years and so there should only be one model in current circulation. The open face helmet has seen some design updates in recent years and therefore there are two marks in circulation at present, the MK10 and MK11. You’ll only need to know which mark of helmet you have if you require spare parts or accessories for it, but how do you know which model you have? The easiest way to tell is to look at the date stamp on the outside rim of your helmet; the date stamp is either shown as two circles (displaying the month and year of manufacture) or a rectangle. If you have two calendar circles, you have a mark 11 helmet – if you have a rectangle, you have a mark 10.