Ball bearing retainers — also known as cages or ball bearing separators — are components in bearings used to separate the balls, maintain spacing and hold the bearings in formation. This prevents ball contact, allowing higher speeds.

Another key function is to help retain grease around balls and raceways. This is essential for smooth running as the lubrication provides a thin film between the contact areas in a bearing to reduce friction, dissipate heat and inhibit corrosion on balls and raceways. The design engineer’s selection of the appropriate cage design for the application is essential in achieving the desired life and performance of the bearing.

This guide will talk you through everything you need to know, from material considerations to operating temperature ranges and corrosion resistance requirements. It also touches on several common problems that can afflict retainers specifically, before addressing some frequently asked questions.

Choosing the best bearing cage material for your application

The retainer is responsible for keeping the rolling elements apart and guiding them. The materials used include steel, brass and plastic. Solid metal cages can be produced using machining techniques, while pressed cages are made from sheet metal. Similarly, plastic cages can be machined from solid plastic or injection moulded plastic.

For greater accuracy and to prevent additional friction, it is important the retainer is not allowed too much radial movement. To achieve this, the retainer is guided by either the balls or one of the rings. In the guide we present seven common bearing retainer types to choose from:

  • Metal crown / ribbon
  • Reinforced nylon crown (TW)
  • Polyethylene crown (PE)
  • PEEK crown (PK)
  • PTFE crown (PT)
  • Nylon crown (PA)
  • Full complement (F/B)

 Frequently asked questions

In this guide, we also answer the most frequently asked questions related to bearing retainers

  • What is the advantage of a ball bearing without a retainer or cage?
  • What causes bearing cage failure?
  • Caged bearings vs loose?

Need to know more? Download your free guide here. Alternatively, contact SMB Bearings on +44 (0) 1993 842 555 or

Our determination to remain specialised gives us a high level of product knowledge, providing bearing and lubrication solutions to existing or potential customers, whether individuals or large corporations. We don’t just sell bearings, we help to solve your problems. - Chris Johnson, managing director of SMB Bearings.