Building closed loops with springy wire
What you are looking for is called spring steel or spring-tempered wire. Tempering is a process where the wire is hardened by heating which allows the resulting spring steel to return to its original shape, despite significant deflection or twisting. When you bend a spring wire, it will maintain a strong, circular loop without kinking anywhere along its circumference.



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To close the the loop, you can use a wire crimp sleeve. They come in many many lengths and diameters, so it shouldn't be too difficult to find one that fits your needs.

 

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