Hello again
I have two NSK NF 305w bearings that are new from my B50, I put in bronze cagged ones in instead as advised by the b50 web site, will the NSK ones be ok in my wm20 on the D/S ,or are there better ones to have
Mark 
email (option): markbrob1@hotmail.com
Hi Mark...The NSK bearings are fine for use in your M20..or your B50 for that matter. It is a common misconception that bronze caged bearings are somehow 'better' than steel or plastic caged bearings when in some examples the reverse is true.
The various cage types are, at the minimum, 'equivalents' and designed to operate in the same environment and carry out the same function as the originals for a given bearing number.
As the steel and plastic cages are dimensionally smaller than the bronze types in some cases (the RHP timing side bearing for example) that allows for the addition of an extra roller...and in that circumstance these types actually have a greater load bearing capacity than the originals.
You might try asking whoever gave you the information the reasoning behind it..I'd be interested to know....Ian
email (option): ian@wright52.plus.com