This is a replacement pinion seal. This is a much better seal than the seals you find at your local parts store because usually they don't have the special dust shield lip. These are really no different than a heavy duty seal other than they do not have an indexing lip for installation. We usually coat the outside of these seals with a little RTV and then press them in.
-Special Lip for dust sealing- Just Like OEM.
There are sizes 29 Spline and 27 Spline