It's probably the best top cap you will ever have. One piece, bolt+topcap with Allen (hex) 5mm socket.
Will fit to every standard starnut.
Not suitable for "expanding" star nuts with the steel coil spring (used in carbon steerer). But it is compatible with ENVE Compression Plug (recommended for carbon steerers).
If your top cap sits from an angle on the stem (does not touch stem with whole circumference), it means your starnut sits from an angle. You will have to make it straight prior to mounting Ab top cap. To do that you can use old steel bolt and a hammer.
Size (Mass +/-1g): only 4g
Key required: Allen 5mm
Material: cnc machined 7075
Dimensions: For measuring purpose treat it like 25mm hex bolt.