Serrated Structure The serrated surface of these thread pieces could have been designed to provide improved cutting performance and efficiency in cutting grass, weeds and light scrub. XL Size - With a length of 185mm and a diameter of 3mm, these thread pieces are larger than traditional replacement thread pieces and could be suitable for heavier mowing and cutting tasks. HIGH QUALITY AND DURABILITY: They could be made of durable material that provides durability and resistance to wear and tear. COMPATIBILITY The thread pieces are probably designed for specific Stihl trimmers or brush cutters to ensure optimal performance and fit use. SPECIALLY DESIGNED FOR TOGEST TASKS The serrated structure and XL size suggest that these thread pieces are designed for more difficult mowing jobs or working with denser and more resistant fouling.