Casio CTK-720 12 Note Rubber Key Contact Strip. Also fits the following models,

CASIO CTK1100
CASIO CTK1150
CASIO CTK1200
CASIO CTK1250
CASIO CTK1300
CASIO CTK1500
CASIO CTK1550
CASIO CTK2000
CASIO CTK2080
CASIO CTK2090
CASIO CTK2100
CASIO CTK2200
CASIO CTK2300
CASIO CTK2400
CASIO CTK2500
CASIO CTK2550
CASIO CTK496
CASIO CTK700
CASIO CTK710
CASIO CTK720
CASIO LK120
CASIO LK127
CASIO LK130
CASIO LK135
CASIO LK136
CASIO LK165
CASIO LK170
CASIO LK190