These are the Traxxas Slash 4X4 Progressive Shock Springs: Front, +20% Rate, Blue (2).
The Slash 4X4’s fully adjustable suspension gives it an edge in any race, and with Traxxas’ progressive-rate tuning springs, you can hone your truck’s handling to an ever greater degree of precision. Custom-wound specifically for Slash 4X4, the tuning springs are available in four rates to suit any setup. The progressive-rate design allows small-bump compliance without compromising big-hit capability, and the white powdercoated finish guarantees lasting good looks. The springs are color-coded to indicate rate, and are sold in pairs in front and rear lengths.