scalloped heart  layering steel thin die for hand roller mill die cut roller mills or electric roller mills (such as the Sizzix  Big Shot Switch )   Spellbinders and Sizzix etc.
 
size ranges from 2 1/2 " - 1/4", and these will shrink to half their size.
 
Here is a link to successfully using the die cuts in a Sizzix machine.
https://vimeo.com/737292992