The cage spaces, not simply separates
A cage maintains rolling-element spacing, guides elements through the unloaded zone and influences lubricant distribution. Its design must suit accelerations and inertia.
Temperature and lubricant compatibility drive polymer choice
Polyamide cages are common at moderate temperatures. PEEK options support higher temperature and aggressive media, but the complete bearing design and lubrication must remain compatible.
Metal cages are not automatically heavy-duty
Pressed steel, machined brass and other metal designs differ in strength, guidance, weight and emergency-running behaviour. The correct choice depends on the application, not only nominal load.