A. This air filter is designed for GY6 scooters and all - terrain vehicles (ATVs) and belongs to the category of air filters. It has a reasonable design and multiple compatible specifications to meet the needs of different users. B. In terms of connection, there are various options, including connection threads, sealing ring sizes, inner diameters, intake pipe diameters, and exhaust pipe diameters of 35 mm, 38 mm, 42 mm, 45 mm, and 48 mm, which can ensure a closer and better fit with various vehicle models. C. It comes in two types: straight - mouth and oblique - mouth, which can adapt to different installation environments and usage scenarios. The flexible design makes installation more convenient. D. Regarding its external dimensions, the caliber is 45 mm, the width is 100 mm, and the height is 120 mm. The overall outer diameter × height is 12 × 10 cm. This size design can ensure the effective filtration of the air filter without taking up too much space. As a motorcycle modification accessory, it features high flow, which can provide sufficient clean air for the engine, contribute to improving the engine's performance and efficiency, make the vehicle's power output more stable, and bring a good riding experience. Whether for daily riding or traveling on special terrains such as beaches, it can perform well. It is a good choice for enhancing the performance of GY6 scooters and all - terrain vehicles.