[TowerTalk] replacement top plate bearing

[John Keating]

I need to replace the rusted out bearing on the top plate of a tower. I see many flanged bearings listed by the usual online retail sources as well as direct from bearing manufacturers that are priced less than those with tower name brands. Are there any particularly critical design features - e.g., eccentric vs concentric vs standard set screw collar; iron vs aluminum flange; double vs triple seal? And at what point should one use a bearing that takes the vertical load in addition to lateral rotational force?