The prefix code 'BK' indicates the use of a caged needle rollers and a bearing which is closed at one end. These are used for shaft-end mounting and the open end is typically not sealed.
When a rolling bearing is needed for a compact and economical design and where it is not practical to harden and grind the housing bore, or where the housing materials are of a low rigidity such as cast iron, aluminium or even plastics - drawn cup needle roller bearings should be considered.
The original drawn cup needle roller bearing employs a full complement of needle rollers. The full complement drawn cup bearing combines maximum load-carrying capability with the advantages of the drawn outer ring. The inward turned lips of the cup are used to mechanically retain the complement of needle rollers, providing their positive radial retention - even though it may be necessary to remove the shaft repeatedly during servicing of the mechanism employing the bearing.
Drawn cup needle roller bearings are also available with one piece steel cages. This design separates and retains the needle rollers whilst also fulfilling the guiding function. The steel cage construction also provides rigidity and minimises wear.