Steve, I just replaced those on my Spicer Pantera units. They are not sold alone, but came as a set of cork seal, retaining ring, and new threaded cap.? They were off the shelf at my local driveline shop, $7 a kit. i.d.=1 1/4"? o.d.=1 3/4"? thickness= 1/4" Spicer part #D3A,? called a 'Dust Cap" Larry