It was originally leather, but 1/8" "O" rings work very well. I had some that came from a Farm & Fleet store before they closed in this area, and have now been using some that came from the plumbing section of Lowes or Home Depot. I bought a small plastic box with 25-50 or some amount in it. I don't know what they are made out of, but so far gasoline doesn't seem to affect them. Remove the old leather packing from the stem and be sure there is none left in the housing, and then I use two of the "0" rings. Have some that have been installed over a year with no problems.