This is a quality solid brass split ring.  

This ring is made from a brass flat bar by skilled Japanese craftsmen. They made it by bending a flat bar rather than pressing it.

If you put a key through direct to a split ring, 3.5mm ~ 4.5mm in diameter of the hole of the key is necessary. 

Material / Solid brass

Color / Matte nickel chrome plated

Size / 27 mm diameter x 2.8 mm x 3 mm width

Weight / 5.5 g