Only one (1) left at this price! Diameter: 4.62cm; PTFE filters are manufactured and certified to be within conformance of EPA PM 2.5 Reference Method Whatman™ PM 2.5 PTFE membrane filter is a high-purity, thin PTFE membrane centered within a sequentially-numbered and chemically-resistant polypropylene support ring for PM 2.5 ambient air monitoring Thermally stable design of the membrane