Features: Excellent upgrade for 540- and 550-size brushed motors with the same diameter and mounting pattern (vehicle must accept pinions with a 1/8" bore) High-quality 4-pole sintered rotor 4mm gold plated bullet connectors High-quality construction with precision ball bearings and hardened steel 1/8" shaft Overview: The Firma 4000Kv brushless motor is a great choice for 1/10 scale 4WD, 2WD, and on-road models running on 2S LiPo power. Featuring a low cog 4-pole 8-magnet rotor design, CNC machined aluminum housing, insulated high purity copper windings, high-quality alloy steel 3.175mm (1/8") output shaft, and precision bearings for high durability and smooth rotation. Preinstalled 4mm gold plated bullet connectors for easy installation, and perfectly matched for the Firma 85A Smart ESC.