The Echo 20BPX72CQ 18" Micro Chisel Chainsaw Chain is a genuine OEM replacement chain specifically designed for the Echo CS-3900/400 chainsaw model. This high-quality chain is compatible with Echo chainsaws and comes pre-assembled, making it convenient for users who don't need to worry about assembly. With a durable construction and precise cutting capability, this chain is an essential tool for maintaining yards, gardens, and outdoor spaces.