I own two Hatsan PCP air rifles and know the importance of quality O-rings for the fill probe first hand.  After doing testing, I am now using these black O-rings that are made from Buna-N rubber that is oil resistant and tolerates the silicone grease we use to lubricate the fill probes just fine.  To get a good seal, their durometer, or hardess, is 70A, which is ideal for high pressure air.

These O-rings should fit fill probes from the following companies (and model if they have more than one size of probe like Air Venturi and Hammerli do):

• Air Venturi Halestorm
• Evanix
• FX
• Hammerli Pneuma
• Hatsan
• Kral
• Logun
• Raider

These are sold in packages of 4 O-rings.  If you order two packages then that means you will get 8 O-rings and so on.

This listing is just for the O-rings.  Any photos of fill probes are for comparison purposes.