It's a stack spacer. It's a top cap. It's both! The Ultralight stem cap is designed specifically for carbon steerers that require that the steer tube extend above the stem.

1 1/8" top (straight 1 1/8" or 1 1/2" to 1 1/8" taper) steerer tubes only

Light-weight and durable 6061-T6 aluminum

S.H.I.S. Stem Clamp Diameter	28.6
Color	Ultraviolet Purple
Includes Star Nut	No
Defined Color	Purple