5 3/4"
i personally run these
with narva +100 (still legal 60/55w) bulbs in the main outside lamps and 130w rally bulbs as a pair of spotlights in the inside lamps. With new wiring, fuses and relays. the light output is comparable with my ba falcon
what ever lamps you get make sure they are semi sealed so you can replace the bulbs with good ones.