The tube for the air inlet is probably not pressure rated. It’s just a wimpy tube for drawing in air (suction).
The tubing Hornblasters sells is DOT tubing - measured by the OD. So yes the ID is smaller. IDK if 1/2" tube would work over a 3/8" barb. That hard tubing is not meant to stretch.
Barbs are usually meant for hose which is measured by the ID.
Perfect! Just wanted to make sure I am installing the right tubing so wont need to replace down the road when I get bigger horns or eventually get a k5la under her