Inside, outside serrations? Types of center lock locking rings

Posted at: Sep. 12, 2022

There are two types of lock rings for center locking disc brakes, inner serration and outer serration. The following is a summary of the differences and how to select the right one.

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There are four types of locking rings for the center lock

Internal serration

This is a type of lock ring that attaches the rotor to the wheel hub and is turned by the saw-tooth (serration) inside the lock ring. The Shimano model number for this type is Y8K198010.

The teeth on the inside of the lock ring are exactly the same standard as those of Shimano’s sprocket lock rings, so a sprocket lock ring turning tool can be used to install the lock ring.

Due to the teeth on the inside, the compatible shaft is limited to 12 mm. If you try to insert a 15 mm shaft, the lockring tool will interfere with the shaft and you will not be able to tighten it properly.

Outer Serration

The outer serration type lock ring is used for shafts that cannot be passed through the inner serration. The Y24698030 is a type of lockring with the teeth on the outside of the ring.

Since the teeth for tightening are on the outside, the hole for the shaft is large enough to use a large shaft (e.g., 15 mm). Also, depending on the wheel hub to be installed, the inner serration lock ring may not fit well, so an outer serration lock ring is used in that case.

Because of the difference in diameter, the lockring cannot be tightened with the sprocket lockring, and must be installed with a tightening tool for “Hollowtech 2,” Shimano’s BB standard.

Internal and external serrations

Locking rings for both serrations are also available. This type of lock ring has teeth on both the inside and outside, and the Shimano model number is Y8JX98020.

You may be thinking, “Why not use both 15mm and 12mm?” However, as explained earlier, even a 12mm lockring with an inner serration lockring may interfere with the lockring during installation, so this lockring is used in such cases.

For AFS hubs

Overseas manufacturers such as Campagnolo and Fulcrum use a different standard center lock from Shimano, called AFS (Axial Fixing System). The rotor splines are the same as those used by Shimano, but there is a difference in the lock ring attachment area.

In the case of Shimano’s center-lock standard hub, the groove for the lock ring installation is on the inside. Therefore, the Shimano lock ring connection has a groove on the outside (to engage the inner groove).

Structure of the mounting part of Shimano Center Lock standard hub

On the other hand, in the AFS hub, the groove where the lock ring attaches is on the outside, and the opposite is true for the lock ring connection: the groove is on the inside.

Looking at the AFS hub, there is a groove on the rotor spline (rotor joint) that is not present in Shimano’s center lock, where the lock ring is installed.

Structure of the mounting part of AFS standard hub

This means that Shimano center lock lock rings cannot be used with AFS hubs.

Lock rings for AFS hubs are usually included with the wheels, so there is no problem if you use those, but if you get used wheels, be sure to check that they come with lock rings.

Differences between Internal and External Serrations and How to Tell Them Apart

Let’s look at a summary of the differences between internal and external serrations and how to tell them apart.

Type Shimano model number How to identify Tools used Compatible shafts
Inner serration Y8K198010 Tooth inside TL-LR15 Up to 12mm
Outer serration Y24698030 Tooth on the outside TL-FC36 Corresponding to 15mm
Internal and external serrations Y8JX98020 Teeth both inside and outside FL-FC36
TL-LR11
Corresponding to 15mm
For AFS hubs - The connection to the hub has teeth on the inside. TL-FC36 may be used. Corresponding to 15mm

Note that some reviews say that the TL-LR15 cannot be used for tools with inner/outer serrations and locking rings.

The headline image of this article shows “inner serration” on the left, “outer serration” in the middle, and “inner/outer serration” on the right. At a quick glance, they look like the same lock ring, but a closer look at the part with the teeth shows a completely different structure.

Key Points in Selecting a Lockring

Based on the differences between inner and outer serrations of lockrings we have seen so far, let’s look at some points to consider when choosing a lockring.

First of all, the thickness of the shaft of the bike you are using determines the inside and outside serrations: if it is 12 mm, it is the inside serration; if it is thicker than 12 mm, it is the outside serration. However, for Shimano wheel hubs, the compatibility chart may specify which lockring to use. Also, if it is an AFS hub, use a special lockring.

Next, check the thickness of the lockring. Depending on the shape of the wheel hub, the thickness of the lockring may interfere with the fork or frame. The thickness is also a matter of compatibility with the wheel, and some wheels may come with a dedicated lock ring, so if so, you can be sure to use that one.

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