For the Diana Model 5 pistol and it's variants. Hyscore 815 etc
The near 1" OD seal.
Not for the latest Magnum Model
If our seal is too tall and does not fit your piston it has been used with a bad seal or dry fired often and the piston head has been compressed and you need to get a new piston or have it remachined to be corrected. That is from abuse.