Fitting a top cap on an expansion plug system is no different than a star nut system. They are standardized across most brands. Unless it is some weird, proprietary design, they accept the same top cap bolt as a star nut.

I'm using the Specialized plug. It is long and supports the entire stem. $9.99 at Amain Cycling. They are a legit shop. I've ordered from them several times and run two of these plugs.



Tightening the large bolt inside the plug expands the plug so that it grips the inside of the steerer. The large bolt is hollow and threaded on the inside. The top cap bolt screws down into the center of the large bolt in the same way it would screw into a star nut. There really isn't a difference.





I actually didn't use the ENVE plug which came with the ENVE fork because I think the Specialized plug offers more support for the stem. The ENVE plug is on the right.

I'd just send the ENVE plug to you if I could find it.