Industrial MRO Reference Library · Technical Reference

Insert Bearing Locking — Set Screw, Eccentric Collar & Adapter

Mounted bearing inserts lock to the shaft by set screws, an eccentric collar or a tapered adapter sleeve. This sheet explains how each method works, where it fits and how to install it so the insert does not spin or walk.

Ref MRO-0010

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

The insert is the ball or roller bearing inside a pillow block or flange unit. It has a wide inner ring that must be fixed to the shaft. Set screw locking uses two set screws in the inner ring that bear on the shaft. Eccentric collar locking (also called cam lock) uses an offset collar that slides over an offset step on the inner ring; turning the collar wedges the ring to the shaft, then a set screw holds the collar. Adapter locking uses a split tapered sleeve and locknut; tightening the nut drives the bearing up the taper and clamps it evenly around the shaft. Other makers offer concentric collar and other clamp designs.

How to identify

Set screw inserts show two screws in the extended inner ring. Eccentric collar inserts have a separate collar on one side with one set screw and a drilled hole or notch for a drift. Adapter inserts have a tapered bore and come with a sleeve, locknut and lock washer. The insert number shows the type; the prefix scheme varies by maker. See mounted bearings, pillow blocks and flange units and bearing numbers decoded.

Locking method comparison

Method	Best for	Limits
Set screw	General duty, one direction or reversing at moderate speed	Screws can mark shaft; may loosen under heavy vibration
Eccentric collar	One direction of rotation	Not for reversing loads; collar must turn with rotation
Adapter sleeve	Heavy loads, vibration, higher speed, easy removal	More parts; takes longer to install
Concentric collar	Reversing duty, less shaft damage than set screws	Maker-specific parts

Key points

Clean the shaft and check its size and finish against the maker's tolerance. Undersized or worn shafts cause creep.
Set screw inserts: tighten both screws to the maker's value. Use the correct hex key, not a worn one.
Eccentric collar: turn the collar by hand in the direction of shaft rotation until it grabs, then tap it tight with a drift and tighten its set screw.
Adapter sleeve: tighten the locknut to the maker's method, which may be turns, angle or clearance reduction, then bend a lock washer tab.
On a shaft with two bearings, lock one and leave the other free to float if the design calls for it.

Common mistakes

Turning an eccentric collar against the direction of rotation.
Using set screw inserts on heavy reversing loads.
Overtightening an adapter nut and removing all internal clearance.
Hitting the insert or housing with a hammer during install.

Governing standards: No single consensus standard covers insert locking methods. Follow the bearing maker's mounting instructions and tightening data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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