If you wear one of these Three Quarter Jet style open face helmets, you need to order a Mk2 cover, or a Spikey cover designed for helmets with an external circumference of 87cm to 92cm
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The Mk 2 and Spikey helmet covers for bikers and motorcyclists
If you wear one of these Half Height Shorty (or Bell cycle) style helmets, you need to order a Mk3 cover, designed for helmets with an external circumference of 80cm to 84cm"
The Mk 3 helmet cover for bikers and cyclists
If you wear one of these Beanie, Novelty, Construction or Adventure Sport style helmets, you need to order a Mk4 cover, designed for helmets with an external circumference of 69cm to 71cm
The Mk 4 helmet cover for skiers, snowboarders, climbers, hockey players, horse riders etc
