Timken employee here a lot of that may have to do with a patent a company has on a specific part. I know we have some parts on our cnc machines that we can'`t use our own bearings on because we can'`t legally make one. I do believe Timken is the best bearing on the market and not just because I work for them. All Timken bearing use Timken steel.
39591/39520 Tapered Roller Bearing 2 5/8'' x 4 7/16'' x 1 3
39591/39520 Single-Row Tapered Roller Wheel Bearing! This bearing carries a radial load simultaneously with an axial load in one direction! This is a popular size that can be used in many applications!
Part Number 39520, Tapered Roller Bearings - The Timken
Browse Part Number 39520: Tapered Roller Bearings - Single Cups - Imperial in the The Timken Company catalog including Part Number:Item Name:Description:Series:Cup Part Number:Design Units:D - Cup Outer Diameter:C - Cup Width:r - Cup Backface "To Cle