Genuine Casio replacement rubber packing/o-ring in black. 
 
Made for the following model(s):
EFR-554SG-2AV, EFR-554RR-2AV, EFR-554D-1A9V, EFR-554L-2AV, EFR-554D-1AV, EFR-554L-7AV, EFR-554D-1A2V, EFR-554D-2AV,
 
GG-1000-1A3, GG-1000-1A, GG-1000-1A5, GG-1000GB-1A, GG-1000RG-1A, GG-1000GB-4A, GG-1035A-1A, GG-1000TLC-1A, GG-1000BTN-1A, GG-1000-1A8, GG-1000WLP-1A,
 
GSG-100-1A, GSG-100-1A8, GSG-100-1A3,
 
GWG-100-1A3, GWG-100-1A8, GWG-100-1A,, GWG-100GB-1A