The ARRMA Metal Input Gear (13T, 1.35M) is a heavy-duty all-steel bevel input gear engineered for ARRMA 4X4 3S, 4S, and MEGA/Boost platforms. 
It serves as a direct replacement for 4S BLX models and a high-strength durability upgrade over the stock composite-tooth gear (#ARA311031) on 3S BLX and MEGA drivetrains.
Tooth Count & Pitch: 13-tooth bevel gear, 1.35 Module (1.35M)
Required Pairing: Must be paired with a compatible 37-tooth 1.35M differential gear set (such as #ARA311152, #ARA311154, or the complete metal diff set #ARA311155).
Verify 1.35M Pitch: Older ARRMA 3S vehicles built before the 1.35M drivetrain revision used 0.8M gears (#AR310886) and are not cross-compatible.