On a gasket die, spring-back, hole form and how the part leaves the sheet matter as much as outline. Gasket cutting knives are used for NBR, EPDM, rubber, foam, felt, EVA, cork and thin metal-backed technical forms. Crush and inner-hole cleanliness affect the job. Inner/outer size, hole diameter, corner radius, thickness and compression allowance are read together. Source: ikramlazer.com gasket page.