NTN 7301C/DF bearing

NTN is one of the world's leading manufacturers of bearing products to OEMs, distributors, and end users.

What is the nomenclature for Precision Bearings (P4, P5, Tolerances)?; What is the difference between T D1 or what is the designation for an oil hole? . Paired arrangements for angular contact bearings are designated as “D2” (universal flush ground pair), “DB” (matched back-to-back pair), “DF” (matched face-to-face