Copper plated over brass, 2mm seamless tube, 1.2mm inside diameter. Sold per pkg of 100.
I started out years ago using only genuine copper crimps and found them to tear too easily. I'm only fond of plated copper when it comes to the practicality of it. This crimp is copper over brass. The brass gives a bit of sturdiness that a crimp bead should have.
*Here's something that works for me when crimping down on metal. Metal likes to snap when it's cold...and you don't want that in a crimp bead! This will sound weird, but I sit on my crimp beads while designing which gives them the perfect temperature when it comes time for me to crimp down on the metal. Yep, you'll feel like a mother hen, but it works.