North N7500-8 Highly Toxic Particulate (HEPA) Respirator Filter (P3) Suitable for Protection from Dusts, Fumes, Mists, Asbestos, Radionuclides, etc. Mini Size Allows this Filter to be Used Under a Welding Helmet Can be Used with a Variety of Air Purifying Respirators Size: 3.1" in Diameter and Only 1.5" Deep. Has a 1" Connection. NIOSH and MSHA Certified