A 20mm stainless steel diesel fuel filter is typically used for inline fuel filtration in diesel transfer systems to remove particulate contaminants, rust, and debris — protecting pumps, injectors, and engines. The 20mm refers to the hose or pipe connection size (≈ 3/4 inch), common in medium- to high-flow setups (e.g., 50–100 LPM). Check seal material – Viton is best for diesel durability. For water-prone environments, go for filters with water separation capability.