The phrase "duty steel" refers to a type of strong and sturdy steel that is designed to withstand heavy use or extreme conditions. It implies that the steel is durable and reliable for tasks requiring strength and toughness. Full definition
It's constructed of heavy duty steel for maximum durability and will give your mattress a lot of support. (geekwrapped.com)
The heavy - duty steel frame folds up for easy storage when not in use. (geekwrapped.com)
New parts include shocks, weather seals, universal joints, exhaust system, mirrors and extreme - service heavy - duty steel wheels with off - road tires. (barrett-jackson.com)