The 42″ brake line is for the Honda Grom dual-fitting (single caliper – junction valve) handbrake kits.
If you have a Honda Grom with a dual caliper bracket and a second caliper, you will need the 65” brake line. That handbrake line is located here:
65” Brake Line for Honda Grom dual caliper handbrakes
Regarding sport bikes, you will need a 56″ brake line, which is used for single caliper (dual-fitting) handbrake kits for street bikes.
If you have a dual caliper setup on a street bike, you’ll need the 80″ brake line.