Mavic introduced a through-axle standard called
"Speed Release."
Frame brands like Cannondale and LOOK use it,
and ENVE adopts it for standalone forks.
↑This is the Speed Release axle that comes with a LOOK frameset,
which uses an Allen key type.
↑One distinctive feature is the stepped, recessed area,
↑and this C-ring-shaped tube (probably made of brass)
that doesn't exist on other axles.
Edit: I received a comment saying "The material of the brass-colored piece is probably phosphor bronze,
which is used for spring material." Many thanks for that.
Let me thread it through a disc front hub.
Since the hub shaft inner diameter has negative tolerance to the axle,
it passes through easily,
but then it catches with a click!
As you push further, this C-ring continues to apply an expanding force
toward the inside of the hub shaft,
←←←the shoulder on this end
→→→and the shoulder on that end.
The axle moves within the width of the recess where the C-ring is seated,
but it won't fall out on its own.
So when you tighten it into a front fork,
the gap between the hub end and the axle will actually be wider than in the image above,
but the axle position when fully tightened becomes fixed in place.
At that point, the threaded end of the axle
passes through the fork's threaded hole,
but when you loosen the Allen key (or lever) side,
the part extending from the hub becomes the narrowly recessed section.
Speed Release-compatible front forks have a cutout on this side
just like quick-release forks, so you can
remove the wheel quickly without pulling the axle out,
leaving the axle in position.
In a race when you get a flat and need to swap wheels at neutral service,
you might need to pull out the axle,
but when you get a flat during practice or riding and need to remove the wheel
at the roadside, you don't have to set the axle down on the ground.
This much is common knowledge, but
Speed Release has even more features.
The axle marking reads M12×2 P1.
I understand the 12mm diameter with 1mm pitch,
but what does this "×2" mean?
It indicates a "double-start thread."
Before explaining double-start threads,
let me start with a single-start thread.
If you wrap one line around a cylinder with the same pitch,
and that line is the thread, that's a single-start thread.
When you have two of these lines, it becomes a double-start thread,
and more than that makes three-start, four-start, etc.
An n-start thread moves the thread
n times the apparent pitch (※) in one complete rotation.
As shown in the diagram, if a single-start and double-start thread
have the same apparent pitch, the double-start moves
twice as much thread distance per rotation.
Speed Release has an apparent pitch of 1.0mm,
so the thread moves 2.0mm per revolution,
which is a larger movement than a 1.75mm pitch single-start thread.
In practice, the front Speed Release comes off with just three turns
(the spec says four, so the manufacturer's design
calls for eight threads maximum).
※The term "apparent pitch" isn't technically accurate.
Regardless of how many starts a thread has,
pitch means the distance between one thread and the next.
Almost nobody has never touched a multi-start thread.
Plastic bottle caps use multi-start threads.
One disadvantage of multi-start threads is "inferior clamping force,"
but in the case of Speed Release,
this works out perfectly, whether intentional or not:
the tightening force is "sufficient to secure the wheel
but cannot be over-tightened,"
landing in just the right sweet spot.
Even if you try to tighten it as much as you would an X-12 through-axle
to the point of damaging hub bearings, with Speed Release
the axle width starts compressing the fork or frame,
and you quickly hit a point where you can't tighten further.
Furthermore, Mavic's lever-type Speed Release axle has
a ratchet mechanism like a torque wrench built into the lever root
that prevents over-tightening no matter what.
Once the lever rotation starts clicking, the clicking no longer converts
to clamping force; it just positions the lever in a nice-looking spot.
With older lever-type quick-releases,
if you tried to clamp with force enough to damage hub bearings,
you'd get the feeling the cam at the lever root would self-destruct,
so it's essentially impossible to apply that much force—
a kind of built-in fail-safe.
Shimano's E-THRU axle is a through-axle standard
that uses a cam-lever for final tightening.
At 12×1.5mm with a coarse thread pitch,
it too, like quick-releases, won't over-tighten bearings.
Speed Release requires the threaded hole side to also be double-start,
so it won't work on incompatible frames or forks.
Probably (and I'm quite confident), people who are completely unaware
that double-start threads and press-fit end hubs have bearings vulnerable
to over-compression might use a Roval front wheel on both
a Specialized X-12 through-axle fork and a Cannondale Speed Release fork
and use them for an extended period.
If the sample size is large enough,
the Specialized fork with the front wheel would definitely show
a markedly higher proportion of bearings with grinding resistance.
"Speed Release."
Frame brands like Cannondale and LOOK use it,
and ENVE adopts it for standalone forks.
↑This is the Speed Release axle that comes with a LOOK frameset,
which uses an Allen key type.
↑One distinctive feature is the stepped, recessed area,
↑and this C-ring-shaped tube (probably made of brass)
that doesn't exist on other axles.
Edit: I received a comment saying "The material of the brass-colored piece is probably phosphor bronze,
which is used for spring material." Many thanks for that.
Let me thread it through a disc front hub.
Since the hub shaft inner diameter has negative tolerance to the axle,
it passes through easily,
but then it catches with a click!
As you push further, this C-ring continues to apply an expanding force
toward the inside of the hub shaft,
←←←the shoulder on this end
→→→and the shoulder on that end.
The axle moves within the width of the recess where the C-ring is seated,
but it won't fall out on its own.
So when you tighten it into a front fork,
the gap between the hub end and the axle will actually be wider than in the image above,
but the axle position when fully tightened becomes fixed in place.
At that point, the threaded end of the axle
passes through the fork's threaded hole,
but when you loosen the Allen key (or lever) side,
the part extending from the hub becomes the narrowly recessed section.
Speed Release-compatible front forks have a cutout on this side
just like quick-release forks, so you can
remove the wheel quickly without pulling the axle out,
leaving the axle in position.
In a race when you get a flat and need to swap wheels at neutral service,
you might need to pull out the axle,
but when you get a flat during practice or riding and need to remove the wheel
at the roadside, you don't have to set the axle down on the ground.
This much is common knowledge, but
Speed Release has even more features.
The axle marking reads M12×2 P1.
I understand the 12mm diameter with 1mm pitch,
but what does this "×2" mean?
It indicates a "double-start thread."
Before explaining double-start threads,
let me start with a single-start thread.
If you wrap one line around a cylinder with the same pitch,
and that line is the thread, that's a single-start thread.
When you have two of these lines, it becomes a double-start thread,
and more than that makes three-start, four-start, etc.
An n-start thread moves the thread
n times the apparent pitch (※) in one complete rotation.
As shown in the diagram, if a single-start and double-start thread
have the same apparent pitch, the double-start moves
twice as much thread distance per rotation.
Speed Release has an apparent pitch of 1.0mm,
so the thread moves 2.0mm per revolution,
which is a larger movement than a 1.75mm pitch single-start thread.
In practice, the front Speed Release comes off with just three turns
(the spec says four, so the manufacturer's design
calls for eight threads maximum).
※The term "apparent pitch" isn't technically accurate.
Regardless of how many starts a thread has,
pitch means the distance between one thread and the next.
Almost nobody has never touched a multi-start thread.
Plastic bottle caps use multi-start threads.
One disadvantage of multi-start threads is "inferior clamping force,"
but in the case of Speed Release,
this works out perfectly, whether intentional or not:
the tightening force is "sufficient to secure the wheel
but cannot be over-tightened,"
landing in just the right sweet spot.
Even if you try to tighten it as much as you would an X-12 through-axle
to the point of damaging hub bearings, with Speed Release
the axle width starts compressing the fork or frame,
and you quickly hit a point where you can't tighten further.
Furthermore, Mavic's lever-type Speed Release axle has
a ratchet mechanism like a torque wrench built into the lever root
that prevents over-tightening no matter what.
Once the lever rotation starts clicking, the clicking no longer converts
to clamping force; it just positions the lever in a nice-looking spot.
With older lever-type quick-releases,
if you tried to clamp with force enough to damage hub bearings,
you'd get the feeling the cam at the lever root would self-destruct,
so it's essentially impossible to apply that much force—
a kind of built-in fail-safe.
Shimano's E-THRU axle is a through-axle standard
that uses a cam-lever for final tightening.
At 12×1.5mm with a coarse thread pitch,
it too, like quick-releases, won't over-tighten bearings.
Speed Release requires the threaded hole side to also be double-start,
so it won't work on incompatible frames or forks.
Probably (and I'm quite confident), people who are completely unaware
that double-start threads and press-fit end hubs have bearings vulnerable
to over-compression might use a Roval front wheel on both
a Specialized X-12 through-axle fork and a Cannondale Speed Release fork
and use them for an extended period.
If the sample size is large enough,
the Specialized fork with the front wheel would definitely show
a markedly higher proportion of bearings with grinding resistance.