Drawn Cup Needle Roller Bearings with Open Ends vs Closed End: How to Choose

When engineers specify a drawn cup needle roller bearing, one of the first decisions is whether the application requires an open end or closed end design. Both types share the same cold-drawn outer cup construction and needle roller geometry, but the presence or absence of a closed end significantly affects how the bearing installs, retains, and performs in service. Getting this choice wrong creates assembly problems, contamination issues, or unnecessary cost.

This article breaks down the structural difference between the two designs, the application conditions that favour each, and the practical assembly considerations that inform the final selection.

What Differentiates Open End from Closed End Designs

An open end drawn cup needle roller bearing — designated in the HK series (metric) and in some BK series variants — has both ends of the cup open. The shaft passes completely through the bearing, entering from one side and exiting from the other. The cup is a thin-walled cylindrical shell with no end cap, and the roller assembly is retained inside the cup by the cup's inwardly-rolled lips at each end.

A closed-end drawn-cup needle roller bearing — the BK series is the primary metric designation — has one end of the cup sealed with an integral formed cap. The closed end is drawn as part of the cup during the cold-forming process, creating a one-piece shell with a flat or domed end. The shaft enters from the open end and seats against the closed end cap, which acts as an axial stop.

In both cases, the cup wall thickness is thin — typically 1–2 mm depending on bore size — and the bearing presses directly into the housing bore for retention. The outer raceway is formed by the inner surface of the drawn cup itself, ground to bearing tolerances after forming.

When to Use Open End Drawn Cup Bearings

Through-Shaft Applications

The defining condition for an open end bearing is a through-shaft: a shaft that must pass completely through the bearing position without obstruction. Gearbox countershafts, transmission layshafts, and spindle assemblies where the shaft extends beyond the bearing on both sides all require open end designs. A closed end bearing physically blocks shaft passage and cannot be used in these configurations.

Open end bearings also suit applications where two bearings are mounted back-to-back on the same shaft journal, with the shaft passing through both. In these arrangements, the rollers of both bearings share the same shaft raceway, and an open bore at each bearing position is essential.

The HK series covers open-end drawn cup needle roller bearings in metric dimensions across a bore range from 3 mm to approximately 35 mm. For larger bores, drawn cup bearings transition to the SCH series (inch dimensions) or machined ring constructions.

Lubrication Access Requirements

Open end bearings allow lubricant to flow freely through the bearing from either side. In splash-lubricated gearboxes where oil circulation carries lubricant to all bearing positions, open end bearings benefit from this flow — oil enters from one side, lubricates the rollers and raceway, and exits from the other. Restricting this flow with a closed end cap can starve the bearing of lubricant in splash-lubrication systems.

For grease-lubricated applications with external grease delivery via nipples or centralized lubrication systems, open end bearings allow grease to be delivered directly to the roller assembly. The open geometry makes it straightforward to verify that grease has reached the bearing interior during maintenance.

When to Use Closed End Drawn Cup Bearings

Blind Bore Housings

The closed end bearing's primary application driver is the blind bore housing — a housing where the shaft bore does not pass completely through the housing wall, terminating in a flat or radiused bottom. Blind bores are common in compact housings where through-bore machining would either break through the housing wall or require complex sealing at the back face.

In a blind bore, an open end bearing would seat with its open bore facing the bore bottom, leaving a gap between the housing bore bottom and the bearing end that provides no axial location for the shaft. A closed end bearing seats firmly in the blind bore with the closed cap contacting the bore bottom (or a small gap for oil), and the shaft seats axially against the closed end cap from inside the bearing. This arrangement locates the shaft axially without requiring a separate shoulder, snap ring, or end cap component.

The BK series covers closed-end drawn cup needle roller bearings in metric dimensions. BK bearings share the same outer diameter and length dimensions as their HK open end counterparts — a BK 1210 and an HK 1210 are dimensionally identical except for the closed end — allowing designers to switch between types without changing the housing bore specification.

Retention and Contamination Control

The closed end cap provides a physical barrier against contaminant ingress from the shaft end of the bearing. In applications where the shaft end is exposed to dust, swarf, or moisture — portable tools, agricultural equipment, outdoor machinery — the closed end reduces contamination entry compared to an open end design. This is not a substitute for a proper seal in heavily contaminated environments, but it provides meaningful protection in moderately dirty conditions without adding a separate sealing component.

The closed end also prevents lubricant from escaping axially out of the bearing's shaft-end face. In grease-lubricated applications, this retains grease within the roller assembly longer, extending relubrication intervals. Combined with a shield or seal at the open end, a closed end bearing can create an effectively sealed grease reservoir without requiring a fully sealed bearing designation.

For applications needing maximum contamination protection, full complement drawn cup needle roller bearings with closed ends are available in both open and closed end configurations — the FY and MFY series — providing the load capacity of a full complement design with the contamination resistance of the closed end geometry.

Load and Speed Differences Between the Two Types

Open-end and closed-end drawn cup bearings with the same bore diameter and length carry identical radial loads, since the roller complement and raceway geometry are the same. The closed end cap does not contribute to or detract from radial load capacity.

Speed limits are also equivalent between open and closed end variants of the same series and size. The closed end cap is a static element with no contact with the rotating shaft or rollers (the shaft seats against it only as an axial stop, not as a rotating contact), so it does not introduce additional friction or speed limitations.

The practical difference in load behaviour is axial: a closed end bearing provides a defined axial stop for the shaft, preventing shaft movement in one direction without additional hardware. An open end bearing provides no inherent axial location — the shaft can move axially through the bearing unless constrained by other means such as shoulders, snap rings, or paired bearings.

Assembly Considerations

Both bearing types press into the housing bore with an interference fit. The installation method differs slightly:

Open end bearings: Install by pressing on the cup rim using a flat-faced installation punch sized to the cup OD. The punch must bear evenly on the full cup rim circumference to avoid distorting the thin wall. Press to the correct depth using a depth stop or feeler gauge — the cup face should be flush with or slightly below the housing bore face per the design requirement.

Closed end bearings: Install with the closed end entering the bore first. The installation punch bears on the open end rim. Confirm that the closed end cap seats correctly at the bore bottom with the specified axial clearance — typically 0.1–0.5 mm to prevent the cap from being loaded as a thrust element during normal radial load operation. If the cap contacts the bore bottom under radial load deflection, it can crack.

For both types, never apply installation force through the needle rollers or cage. Force applied to the inner assembly rather than the cup rim will damage the rollers and deform the cage before the cup has fully seated. Use a properly sized press punch and apply force only to the cup end face.

Shaft insertion into either bearing type should be done carefully to avoid cocking the shaft and scraping the needle rollers. For through-shaft open end bearings, ensure the shaft end chamfer is smooth and properly sized to guide entry without catching on roller ends.

Conclusion

The choice between open end and closed end drawn cup needle roller bearings comes down to three questions: Does the shaft pass through? Does the housing bore have a closed bottom? And is axial shaft location needed without additional hardware? Through-shaft and circulation-lubricated applications call for the open end HK series. Blind bore housings, self-locating shaft applications, and environments requiring modest contamination protection call for the closed end BK series.

Both types share the same compact cross-section, high radial load capacity, and cost-effective cold-drawn construction that make drawn cup needle roller bearings the dominant choice in compact mechanical assemblies across automotive, power tool, and industrial machinery applications.

To compare open end and closed end configurations across the full bore size range, visit our drawn cup needle roller bearing product page for dimensional tables, load ratings, and series availability.