Three New Headsets and a Bottom Bracket for 2026

Internal cable routing has become the default on performance road and gravel frames. But “internal” covers a lot of ground. 

There’s a meaningful difference between a headset designed for frames where cables run fully enclosed from stem to fork crown, and one that solves the routing problem for frames that weren’t originally designed with internal routing in mind.

First Components is debuting three new headsets and a new bottom bracket at Taipei Cycle 2026, starting March 25. Here’s what each one is designed to do.

Full Internal vs Semi-Internal: What the Terms Actually Mean

Fully internal vs semi-internal cable routing: the terms have taken up residence in every bike brand and PM’s vocab. But the terminology is used loosely and it’s worth being precise about what each means.

Full internal routing means cables are completely enclosed throughout the entire path, from the stem, through the head tube, and down to the fork. Pretty clear.

Semi-internal means cables are routed inside the head tube but may exit or be partially exposed at transition points. 

On most semi-internal headsets currently on the market, cables still pass through the bearing assembly itself. 

What makes FIRST’s new headsets unusual is that they route cables outside the bearing that simplifies the bearing design, broadens frame compatibility and makes assembly a bit easier.

R554A-1: Full Internal Routing

Fit: IS52/28.6 upper | EC49/40 lower
Steerer: 1-1/8″ to 1.5″ tapered
Weight: 141g

The R554A-1 is a full internal routing headset: cables pass through the bearing assembly, keeping the cable path completely enclosed from stem to fork. It is designed for frames built around internal cable routing.

One specific compatibility note: the R554A-1 is built to work with ENVE’s IN-Route stem system. When the full system comes together—frame, stem, and headset all specified for internal routing—the result is a completely clean cockpit with no cables visible between the stem and the top of the fork, and no external ports on the cup face.

The upper bearing sits in a 52mm top nut with a 52/49.6mm bearing OD, geometry designed to accommodate cable outers passing through the assembly while maintaining bearing integrity.

S561: Semi-Internal Routing, Outside the Bearing

Fit: ZS52/28.6 upper | IS52/40 lower
Steerer: 1-1/8″ to 1.5″ tapered
Weight: 126g
Cable ports: Ø5.8mm × 4

The S561 takes a different approach to semi-internal routing. Rather than passing cables through the bearing, cables route outside the upper bearing via four Ø5.8mm ports in the cup. They enter the head tube from above, pass alongside the bearing cup, and continue down through the head tube to the fork.

This outside-the-bearing path is what distinguishes the S561 from most semi-internal headsets on the market. Because the bearing design isn’t constrained by the cable path, the S561 works with a wide range of standard frames and stems. 

No proprietary system required.
At 126g it’s also the lightest of the three headsets, reflecting the simpler bearing unit.

T522A-4: Internal Routing Solution for ZS44 Head Tubes

Fit: EC44/28.6 upper | EC44/40 lower
Steerer: 1-1/8″ to 1.5″ tapered
Weight: 183g

The ZS44 head tube is a standard spec found on many frames — but it was not originally designed with internal cable routing in mind. The T522A-4 is a purpose-built solution that allows frames with ZS44 head tubes to run internal cable routing where none was previously practical.

The Backstory: Steerer Tubes, Not Cables

The ZS44 (Zero Stack 44mm) standard gained prominence in the late 2000s and early 2010s. At that time, the industry was transitioning from straight 1-1/8″ steerers to tapered steerers (1-1/8″ top, 1.5″ bottom). 

The 44mm internal diameter was the “magic number” because it was just large enough to:

Fit a Zero Stack cup for a 1-1/8″ steerer.
Fit an External Cup (EC44) for a 1.5″ tapered steerer.
Fit an External Cup (EC44) for a 1.5″ tapered steerer.

Internal cable routing through the headset has only recently become mainstream design requirement of course, primarily driven by the aero-road and clean-cockpit trends of the late 2010s.

The Physics of Space

To route cables through a headset, you need “dead space” between the fork’s steerer tube and the inner wall of the head tube.

A standard tapered steerer is 28.6mm at the top. A ZS44 head tube has an internal diameter of 44mm. This leaves about 7.7mm of clearance on either side, which sounds like a lot until you realize you have to fit a bearing race, the bearing itself, and a compression ring in that gap.

The Modern Workaround

Because ZS44 is so common on steel and titanium frames, companies had to get creative to “retrofit” internal routing into this standard. They often use ultra-thin compression rings or specialized upper covers to squeeze cables through, but it is a tight fit. 

Most modern frames designed specifically for internal routing have moved toward larger standards like ZS56 or IS52 (52mm) to give those cables more breathing room and prevent them from rubbing against the steerer.

Feature	ZS44 Original Intent	Modern Integrated Routing Needs
Primary Goal	Accommodate tapered steerers in straight tubes.	Hide cables from wind and for aesthetics.
Typical Steerer	1-1/8″ to 1.5″ Tapered.	1.5″ Straight or D-Shaped steerers.
Space Constraint	Tight; minimal clearance for extra hardware.	Requires larger bearings (52mm+) for cable paths.

It’s a classic case of the industry hacking an old reliable standard to do something its creators never envisioned.

The FIRST Components Approach

Cables pass through the bearing assembly on this model—the same approach as full internal routing headsets—rather than around it. The EC44 cup OD at both ends is the defining fit spec for this head tube standard.

The higher weight relative to the S561 (183g versus 126g) reflects the taller stack height of 39.4mm versus 17.2mm, which the ZS44 frame geometry requires. This is a compatibility solution for an existing frame category, not a general-purpose headset.

M47SN: T47 External Bottom Bracket, Slim Sleeve

Standard: T47 External (M47×P1.0)
Shell width: 68mm and 73mm
Spindle: 24mm (Shimano-compatible)
Bearings: 6805 (25×37×7mm)
Weight: 123g

The M47SN is a T47 external bottom bracket, and its defining feature is the slim-sleeve design. The reduced sleeve diameter creates more clearance inside the bottom bracket shell, enough to accommodate larger cable runs, including the oversized connectors found on some e-bike systems. For builds where cable or connector diameter has previously forced compromises, this matters.

The threaded T47 standard (M47×P1.0) means installation and removal without bearing extraction tools and without risk to a carbon shell, the core advantage over press-fit that has driven T47 adoption across performance frame builders. The M47SN suits frames where the builder wants T47’s serviceability without the additional sleeve depth of an internal design.

The 6805 bearing (25×37×7mm) is a well-established spec in this application. Available for 68mm and 73mm shell widths. It’s compatible with standard Shimano tools, so no wrench is included.

Choosing Between the Headsets

The selection logic follows the frame specification.

For frames designed for full internal cable routing the R554A-1 is the correct choice. Builders using ENVE’s IN-Route stem have a confirmed compatible system.

For standard head tubes with internal cable routing channels and no proprietary stem requirement, the S561 is the broader-compatibility option. Its outside-the-bearing cable path is the key differentiator, being simpler to work with, lighter, and compatible with a wide range of stems.

For ZS44 head tubes on frames that weren’t originally designed for internal routing, the T522A-4 is the purpose-built solution, a practical means of achieving a clean internal cable run on this head tube standard.

All four products will be on display at Taipei Cycle 2026 from March 25.

Builders working on 2026 or 2027 spec builds can request samples through the First Components contact page.