I need a fuel cap for a Honda UMK435UE brushcutter. Its shown in your diagram as part no5, but there is no part number, price or detail.

I have had a look for you and this should be the correct one you need: https://www.lsengineers.co.uk/fuel-tank-cap-for-honda-gx22-gx25-engines-replaces-17620-zm3-063.html