Why accessories matter
An interference fit stops a ring from turning on its seat, but it does not stop the ring moving along the shaft. Axial location needs a shoulder on one side and a retaining part on the other. For bearings on plain shafts with tapered seats, the accessory can also be what creates the fit. In every case the accessory carries real forces, so it must match the bearing and the shaft thread, and be locked against loosening from vibration.
The parts are small and inexpensive compared with the bearing, which is why they are often overlooked when a program is quoted. A kit without the right lock nut or sleeve leaves the equipment maker with a bearing that cannot be installed. When you source bearings from the desk, list accessories at the same time, as part of the bearing accessories range or a bearing kit.
The main parts
| Part | Common code | What it does |
|---|---|---|
| Lock nut | KM, HM, N | Threads onto the shaft to clamp the bearing ring against a shoulder |
| Lock washer | MB, W | Tab washer that sits behind the nut; a tab bends into a nut slot to prevent loosening |
| Adapter sleeve | H, with a thread | Tapered split sleeve that mounts a tapered-bore bearing on a plain shaft |
| Withdrawal sleeve | AH | Tapered sleeve used to mount or remove a bearing on a stepped shaft |
| Thrust washer | Flat or flanged | Takes axial load between rotating parts |
| Snap ring (circlip) | Internal or external | Axial stop in a groove on the shaft or housing |
Codes follow the common industry system, but different plants may add their own series prefixes. Always state the accessory together with the bearing designation, and confirm the match from the supplier datasheet.
Lock nuts and lock washers
A KM-type lock nut has a ring of slots around its outer diameter and a set screw or tab arrangement. It is used with an MB-type washer, which has an inner tab that locates in a groove cut along the shaft thread, plus several outer tabs. After tightening the nut to the right position, one outer tab is bent down into a nut slot, and the nut cannot turn without breaking the washer. This simple mechanical lock is standard on gearboxes, machine tools and many industrial shafts.
The nut needs a precisely cut thread, correct squareness of the face, and the right thickness. The tightening angle or torque should come from the manufacturer; overtightening can distort a thin inner ring, and an under-tightened nut allows creep. Threads are typically metric fine pitch, and the thread must be cut to the right tolerance on the shaft. Reusing a bent washer tab is bad practice, as the tab fatigues and can crack. Replace the washer at each reassembly.
Adapter and withdrawal sleeves
Some bearings, such as spherical roller bearings and self-aligning ball bearings, are made with a tapered bore (usually a taper of about 1 in 12 on the diameter). A tapered sleeve fits between the bearing and a plain shaft. As the nut is tightened, the bearing is pushed up the taper, which expands the inner ring and creates the interference fit. This allows mounting on a standard, easy-to-machine shaft with a looser diameter tolerance, and lets the bearing be adjusted to the correct internal clearance reduction during mounting.
An adapter sleeve (code H) is used on plain shafts without a shoulder. It can be positioned along the shaft, which is why it is common on long drive shafts and line shafts. A withdrawal sleeve (code AH) is pulled from the other end, and it is used where a shaft shoulder exists and the bearing sits against it. Both sleeves need a matching lock nut and washer; the sleeve thread and nut must match. Getting the pair right at order stage avoids waiting for a missing small part.
Thrust washers, spacers and circlips
Thrust washers are flat hardened or bronze discs that carry axial load between parts, such as in gears or pulleys. The material and hardness matter: steel washers for high load, bronze or polymer for lighter or non-lubricated duty. Spacers set the distance between bearings or other parts and must be ground flat and parallel, because a spacer with out-of-parallel faces tilts the bearing. Snap rings, also called circlips, sit in grooves on shafts or housing bores and act as axial stops for light loads. They are inexpensive but have limited capacity; large axial forces need a shoulder or nut instead. A bearing washer is also part of thrust bearings; see thrust ball bearings.
How to match accessories to a bearing
- Start from the bearing designation and bore type: cylindrical or tapered.
- For a tapered bore, decide between an adapter and a withdrawal sleeve based on the shaft.
- Select the lock nut and washer for the sleeve thread or the shaft thread.
- Check the shaft: thread size, groove for the washer tab, shoulder diameter and squareness.
- List seals, end covers and housing parts that share the same shaft size.
The housing side matters too, as covered in bearing housing types. When the shaft size and the bearing designation are known, the accessory list is usually quick to produce.
Common installation errors
Several failures recur. A nut tightened against a shoulder that is not square pushes the inner ring out of line and the bearing runs hot. A washer tab bent into the wrong slot, or not bent at all, gives only the appearance of a lock. A sleeve mounted without checking the clearance reduction on a spherical roller bearing can leave the bearing too tight, and the heat then shortens its life. Mixing parts from different series, where thread pitch or tab positions look close but differ, is another cause of loosening. The remedy is simple discipline: use matched sets, follow the supplier mounting guidance and measure the clearance or axial drive-up where it is specified.
Quality points when sourcing
Accessories look simple, but quality varies. Check thread form and fit with a gauge, the flatness of the nut face, hardness and finish of washer tabs, and the fit of the sleeve slit. Corrosion protection matters as well, and finishes include oil, phosphate or plating. Packing should keep sleeves, nuts and washers matched to each bearing in the box, or the kit will be mixed up on the shop floor. Reference MOQs and lead times for stock accessories are on the MOQ and lead time page and are confirmed in writing for each order. Send the bearing designation and shaft details through the quote form, and the desk will list the matching accessories.