So, I have a Cannondale Six-13 with carbon steerer tube. The frame came with a compression plug (first pic) but is missing the top cap. I went to the LBS, and bought a Reynolds OUZO compression plug, but the way it's designed, only one end expands, which seems like it will give a pretty small contact area inside the steerer tube because it will not expand evenly. The plug I have expands from both ends and the expanding part is about 30 % more surface area than the Reynolds. Is the Reynolds safe ? I think something like the Pinarello (bottom link) would be the best.

Thoughts ? Can I find a cap for whatever brand plug I have ?



Reynolds:


Pinarello:

The top cap and plug are primarily present to set the preload on the headset bearings. Any of the ones you mentioned will work.

The plug needs to be tight enough to resist the upward pull of the bolt passing through the top cap so you can generate a compression force by drawing the fork upwards. Neither is structural, once the stem is tightened in position the top cap is mostly cosmetic, though it could keep things together should your headset become really loose.

-j

In my opinion the compression plug does play a structural role, if designed to support the backside of the steer tube it helps protect a carbon steer tube from crushing or cracking. I think the Pinarello plug, shown above, is similar to the Colnago plug, and when set behind the stem clamp supports the back side of the steer tube.
The first example "already in the fork steerer" looks like an FSA plug which does not offer as much support.

That's what I was thinking ... that the plug adds strength to the steerer, especially if it's at the same location as the stem.
But I don't have much carbon experience.