Danfoss / Eaton Spare Part O-Ring

It's a spare part meant to be kept on hand for the E-Z Clip nipple assembly. The nipple already comes with two black o-rings installed, and those are not supposed to be removed or swapped out. This particular o-ring is the one associated with the fitting assembly as a serviceable spare, and it's compatible with refrigeration and A/C system compressor oil, which is used during installation to lubricate the nipple before insertion.

This o-ring is indeed designed for use in refrigeration and A/C systems, specifically with compressor oil.

For the E-Z Clip nipple assembly, the two black o-rings on the nipple are a specific rubber compound and size and they should not be removed or replaced. So this spare part o-ring is not meant to swap onto the nipple assembly o-rings.