Shimano Freehub Body Standards Explained: HG, Micro Spline, and XD Compatibility

Shimano Freehub Body Standards Explained

When buying a new wheelset or swapping a cassette, freehub body compatibility is one of the most confusing specifications to get right. HG, Micro Spline, XD — these three terms represent different freehub body standards that determine which cassettes can be installed on your wheelset. This article provides a complete comparison of these three standards.

What Is a Freehub Body?

The freehub body is a component on the rear hub that:

1. Accepts the cassette: The cassette slides onto the freehub body
2. Provides one-way drive: It engages the rear wheel when pedaling and spins freely while coasting (the source of that freewheel clicking sound)
3. Defines the interface: Different freehub bodies have different spline shapes, determining which cassettes can be fitted

1. HG (HyperGlide)

History and Current Status

HG is the standard Shimano introduced in 1989, and it remains the most widespread freehub body standard on the market today.

Technical Specifications

Item	Specification
Number of splines	10 (unevenly spaced)
Body material	Aluminum alloy or steel
Pawl mechanism	Built into the freehub body
Compatible speeds	8/9/10/11-speed
Smallest cog	11T

Compatible Cassettes

Speed	Shimano Cassette	SRAM Cassette	Notes
8-speed	CS-HG200-8	PG-830	Spacer required
9-speed	CS-HG400-9	PG-950	Spacer required
10-speed	CS-HG500-10	PG-1050	Spacer required
11-speed	CS-R7000 / CS-R8000	PG-1170	No spacer needed

Important: When installing an 8/9/10-speed cassette on an HG freehub body, you need to add a 1.85mm spacer, since these cassettes are narrower than 11-speed cassettes.

Limitations of HG

• 11T minimum cog: This is a physical limitation of the HG standard. The diameter of the splines means the smallest cog cannot go below 11T
• Aluminum notching: High-torque pedaling can carve grooves into an aluminum freehub body, making cassette removal difficult. Steel freehub bodies avoid this issue

2. Micro Spline

History and Current Status

Micro Spline is the new standard Shimano developed in 2018 for 12-speed drivetrains, first appearing on the XTR M9100 groupset. It is now also used in 12-speed road drivetrains.

Technical Specifications

Item	Specification
Number of splines	23 (fine-tooth design)
Body material	Aluminum alloy
Pawl mechanism	Built into the freehub body
Compatible speeds	12-speed
Smallest cog	10T

Compatible Cassettes

System	Cassette Model	Gear Range	Application
Dura-Ace R9200	CS-R9200	11-30T / 11-34T	Top-tier road
Ultegra R8100	CS-R8100	11-30T / 11-34T	High-end road
105 R7100	CS-R7100	11-34T / 11-36T	Mid-tier road
XTR M9100	CS-M9100	10-51T	Top-tier mountain
XT M8100	CS-M8100	10-51T	High-end mountain
Deore M6100	CS-M6100	10-51T	Mid-tier mountain

Why Was Micro Spline Necessary?

The 10T smallest cog is the key. A 12-speed cassette needs to fit more cogs into a limited width, and if the smallest cog were still 11T, the overall gear range would be restricted. The 10T cog lets Shimano offer a wider gear range (such as 10-51T) while keeping the cassette compact.

The 23-tooth fine spline design of Micro Spline also solves another problem present in HG: more even load distribution, which reduces the notching issue seen on aluminum freehub bodies.

3. XD / XDR (SRAM)

History and Current Status

XD is SRAM’s proprietary standard, introduced in 2012. XDR is the road bike version, with additional thread length.

Technical Specifications

Item	XD	XDR
Application	Mountain bike	Road bike
Installation	Threaded	Threaded
Smallest cog	9T	10T
Compatible speeds	11/12-speed	12-speed
Cassette retention	Cassette threads on as a unit	Cassette threads on as a unit

Design Differences

XD/XDR is fundamentally different from HG and Micro Spline:

• HG / Micro Spline: Individual cogs slide onto the freehub body one by one and are secured with a lockring
• XD / XDR: The cassette is a single unit (or semi-unit) that threads directly onto the freehub body

Compatible Cassettes

System	Cassette Model	Gear Range	Freehub Body
SRAM Red AXS	XG-1290	10-28T / 10-33T	XDR
SRAM Force AXS	XG-1270	10-28T / 10-36T	XDR
SRAM Rival AXS	XG-1250	10-36T	XDR
SRAM XX1 Eagle	XG-1299	10-52T	XD
SRAM X01 Eagle	XG-1295	10-52T	XD

Compatibility Summary Across the Three Standards

Cassette System	HG	Micro Spline	XD/XDR
Shimano 8-11 speed	Yes	No	No
Shimano 12-speed road	No	Yes	No
Shimano 12-speed mountain	No	Yes	No
SRAM 10-11 speed	Yes	No	No
SRAM 12-speed road	No	No	Yes (XDR)
SRAM 12-speed mountain	No	No	Yes (XD)
Campagnolo N3W	No	No	No (proprietary)

Adapter Options

Swapping the Freehub Body on Your Wheelset

Most mid-to-high-end wheelset brands offer interchangeable freehub bodies:

Wheelset Brand	HG	Micro Spline	XDR	Swap Method
DT Swiss	Yes	Yes	Yes	Pull-off style (most convenient)
Zipp	Yes	Yes	Yes	Pull-off style
ENVE	Yes	Yes	Yes	Pull-off style
Shimano	Yes	Yes	No	Requires special tools
Campagnolo	No	No	No	N3W only, not interchangeable

DT Swiss’s freehub body system is currently the most convenient adapter solution. Its Ratchet EXP hub lets you swap the freehub body by hand, completing an HG ↔ Micro Spline ↔ XDR conversion in under 30 seconds.

Adapter Options

Some manufacturers offer adapters that let non-native cassettes fit onto a different freehub body:

• HG cassette → Micro Spline freehub body: Some third-party adapters exist, but this is not recommended (it affects shifting precision)
• Micro Spline cassette → HG freehub body: Physically impossible (the 10T cog cannot fit)

Recommendations When Buying a Wheelset

1. Confirm your drivetrain system first: This determines which freehub body you need
2. Prioritize wheelsets with swappable freehub bodies: You won’t need to replace the wheelset when you upgrade your drivetrain later
3. DT Swiss hubs offer the best compatibility: All three freehub body types are available
4. Pay attention to end cap spacing: Different frame rear axle standards (130mm/135mm/142mm/148mm) also affect freehub body selection

Future Trends

• HG is gradually being phased out: As 12-speed systems become mainstream, HG’s 11T limitation makes it less suitable
• Micro Spline is expanding: More and more third-party wheelset brands now support Micro Spline
• XD/XDR remains stable: The only option for SRAM users, with a steady market share
• Campagnolo N3W: Developing independently — relevant only to Campagnolo users

Conclusion

Ultimately, your choice of freehub body standard depends on the drivetrain system you use. If you’re building a bike or upgrading your wheelset, the safest approach is to choose a hub system that supports a swappable freehub body. That way, no matter which brand’s drivetrain you switch to in the future, you only need to replace the freehub body — saving you the substantial cost of replacing the entire wheelset.

Related Reading

• Shimano Cassette Lockring Specifications: A Complete Guide
• Complete Guide to Cassette and Chainring Compatibility: Understanding Drivetrain Pairing Logic
• Comparing Hub Ratchet Systems: DT Swiss Star Ratchet vs. Shimano vs. Others
• Freewheel vs. Freehub: A Complete Breakdown of the Differences