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

Wolf Tooth Ultralight Stem Cap with Integrated Spacer Headset Top Cap UPC: 812719020657