DigiKey part number 4094-CD21NA-BK-ND, Hummel AG part number CD21NA-BK
This part number does not come with an O-ring. The O-ring part number is OR-34-BN.
DigiKey does not carry part number OR-34-BN but can be found in this link. Buna-N O-Ring 3/4" NPT | OR-34-BN | Sealcon