Many customers ask why steel drums have two hoops (swedges or rolling rings) in the body of the drum and some have three. While current Performance Standards do not dictate a specific number of rolling rings, it is common to find two rolling rings in Closed Head and Non-Hazardous Material Open Heads, while the Hazardous Material Open Heads most commonly have three. By expanding or stretching the metal, these rings create horizontal creases in the steel, which reinforce the strength of the container and increase rigidity. The oddly placed third ring of the Hazardous Materials Open Head serves to increase the test capabilities of the open top by helping to absorb the shock of the test drop.
HazMat