This is a Hot Racing 57T Arrma 4x4 BLX Steel 0.8MOD Spur Gear, an optional steel Spur Gear for many Arrma vehicles. 

• Rugged 32 pitch (0.8 module) for total reliability when using high power brushless systems
• CNC machined and lightened hardened steel construction
• Replaces factory plastic gear
• Black oxide coating for durability and corrosion resistance
• Can uses factory slipper pads (AR310790) (AR310908) or Hot Racing ATF15H ATF15HN aluminum slipper pad(s)

Number of Teeth: 57

Gear Pitch: 32 pitch (0.8 module)

Tooth Face width: 0.24 inch (6mm)

• Big Rock 4X4 3S BLX: AR102711
• Granite 4X4 3S BLX: AR102666
• Senton 4X4 3S BLX: AR102668
• Typhon 4X4 3S BLX: AR102696

• Arrma Big Rock 3S BLX
• Arrma Granite 3S BLX
• Arrma Senton 3S BLX
• Arrma Typhon 3S BLX
• Arrma Typhon 4X4 550