This is pair of Ofna .21 Silcone Exhaust Round Port Seals.

FEATURES:
Made of a silcone material
Seals the area between the exhaust port to the exhaust header (manifold)
Flanged in the front for a more secure seal

INCLUDES:
Two exhaust seal rings

SPECS:
Inside diameter:  .60"   (15mm)
Outside diameter:   .70"    (17mm)