Spirotek filters are particularly suitable for use with the Spirotek FM9500 full face mask ranges and halfmask HM8500. Spirotek filters have a 40 mm EN148-1 thread connection. P3 Particle Filter has exceptionally low breathing resistance to provide comfortable and long duration use. Spirotek filters include: P3 particle filter, gas filters A2, E1, K1, ABEK1 and combined filters A2P3, A1B1E1K1P3, Hg-P3.