This style of packing ring is used in higher pressure applications where the seal ring is made
from a thermoplastic material, including filled PTFE. At these pressure ranges a backup
ring is required to support the sealing ring at the bore to prevent extrusion. The packing
groove is not wide enough to utilize the Type 210 pair of rings with a backup. Therefore one
ring replaces the normal pair and serves as a radial and tangent combined.
