The Supernova E3 Pure headlight measures only 49mm front to back because it eliminates the switch. So the housing is much smaller. Since better quality hub dynamos all have extremely low drag, many cyclists run their dynamo powered lights "On" all the time, so why even have a switch? Designed to mount at the fork crown on forks with a drilled hole. Compatible with sidepul caliper brakes, as well as disc brakes and most V brakes. Not compatible with old style cantilever brakes. Also available with handle bar mount.