I REALLY like how these pump seals are beefier than the seal that Sheridan put in their airguns, as is stated in the item description.
As is also stated, the brass seal support disc will NOT fit inside these seals properly. Since I don't own a lathe, my fix took 3-4 10mm washers, spot welding them together & smoothing them out with a file to create a smaller diameter support disc. Worked great for me! ^^