This is a felt buffer strip mounted on a foam backed plastic self adhesive strip. The keys come to rest on ( part 170 on schematic )

Whilst not an exhaustive list popular models which use this part include :

P70

P115

YDPS30

YDP131

YDP140

YDP142

DGX660

DGX650

DGX640

DGX630

DGX620

MM8