These oil seals are created from a low-temperature tolerant compound. Benefits include:
Jiri George Drobny, in Fluoroelastomers Handbook (Second Edition), 2016
Types of Oil Seals in Application
4. Seal characteristics

The sealing lip is always made of a rubber or synthetic material. For oil seals with a rubber outer case (R, RST, GR, GRST), the rubber quality of the sealing lip and the outer case are the same.
Overall, the 25x47x7 oil seal is a critical component in many machines and engines, offering durability, reliability, and versatility in sealing oil leaks. By choosing a high-quality oil seal and following proper installation and maintenance procedures, machine operators can benefit from optimal performance and efficiency in their equipment.
Extrusion and Nibbling
• Super helix seal (seal with one-way two-step screw)
MH: O.D. wall is a rubber material
HM: O.D. wall is a metal case
MH(S)H: O.D. wall is metal with a reinforced inner metal case