These are Revolver Supply Premium moon clips. They are designed to work in the S&W 627 8 shot chambered in 38 Spacial/357 Magnum; aka S&W 327 and TRR8.
They are 0.025" thick, made from high carbon steel and are heat treated and a protective blued finish is applied.
They have been tested with Remington, Federal and Starline brass. They are too thick for Winchester Brass.
These are useful if you have the moon clip holders that have magnets to hold the loaded moon clips.
These clips are NOT made to fit Hornady Critical Defense & Speer Gold Dot ammo!