Narrow RC10B4 chassis. The length is +10mm longer than the factory B4.1 chassis and +2mm longer than the factory B4.2 chassis. Accepts "shorty" style battery pack only. Works with JConcepts B5 Silencer (rear motor) and RB6 Finnisher bodies. I recommend using a DE racing B4 chassis brace
https://www.deracing.net/store/index.php?route=product/product&keyword=b4&category_id=0&product_id=350 .