I needed 4 lengths for mine and the guy helping me I asked him to snap it together so I could buy it. They had about 20 pieces in stock and after he mangled 15 of them beyond use I grabbed 4 and took them home and did them myself.
The trick is to make them oval shape and then even slightly heart shaped at the joint. Once you get them locked I take pliers and crimp each end a little. Then round them back up. I used aluminum tape on the joints.
The dryer stuff isn’t as bad as the water heater exhaust steel stuff.