These porous discs for use in fabrication of special glass apparatus. They are available in Chemglass Fine (F), Medium (M), Coarse (C) and Extra-Coarse (XC) porosities. Please see ILPI's Glassware Gallery for a porosity size comparison chart by manufacturer. For general filtering needs, M is the best all-around choice. If you are removing large material, C or XC will give the best throughput.
These discs are designed for low pressure vacuum filtration or gas flow. The maximum pressure differential is 15 psi. Fritted glass discs should not be exposed to excessive temperature changes or direct flame as they have less thermal shock resistance than standard borosilicate glassware.
The thicknesses of these discs vary with size and porosity. Smaller diameter discs are thinner. For example, the 40 mm discs are approximately 3.5 mm (fine), 4.0 mm (medium), 4.0 mm (coarse), and 4.25 mm (extra coarse) thick.