Honda genuine part number 46993-SL0-J01. Part 24 on diagram.
The clutch damper damps vibration through the clutch pedal as the clutch pedal is pressed. The NSX-R (performance model of the NSX sold in Japan) replaces the clutch damper found in the standard NSX with a lightweight block with out the damper mechanism built in. Removing the damper results in faster clutch actuation and additional throw at the fork.
The clutch damper delete assembly is plug-and-play on the standard NSX.