The ZeroRC SR-OP-10 (often identified as the OP Spring Kit 6mm or listed as part of the RW-OP-11 or SR-OP-9 series) is an optional suspension spring set designed for the RW00 and RW00SR 1/24 drift chassis. 
 
Key Specifications & Features:
 
This kit is intended for fine-tuning the vehicle's suspension response,
particularly for competitive micro-drifting: 
Spring Count: Typically sold as a comprehensive set of 18 pieces.
Dimensions: Features a 6mm diameter specifically sized for ZeroRC metal shock absorbers.
Hardness Tiers: Springs are color-coded into three distinct hardness levels to suit various track surfaces (like P-tile, carpet, or concrete):
Pink: Soft
Green: Medium
Yellow: Hard
Length Variations: The set includes 3 different lengths for each hardness level, allowing for diverse ride height and pre-load configurations. 
 
Performance Impact:
 
Upgrading to the 6mm OP spring set allows drivers to:
Adjust Weight Transfer: Softer springs can increase body roll and rear-end "squat" for more traction, while harder springs provide a more responsive, sharp steering feel.
Optimize Rotation: According to ZeroRC's official design philosophy, these springs help balance the vehicle's rotation speed when entering and exiting corners.