The open-face filter holders are lightweight and corrosion-resistant. Available in three sizes: 25, 37, and 47 mm. Includes caps. The 25 mm holder is made of Delrin plastic and is designed for clean room sampling, breathing-zone air samples collecting, bacterial monitoring, particulate analysis, etc.The 37 and 47 mm holders are constructed of aluminum. They can be used for trapping airborne particles, fluorescent tracers, and other contaminants. They include a plastic cap that protects samples after filtration. This product is not approved for use in medical, clinical, surgical or other patient applications.