MicroPlus-31 STL membrane circles black, for Membrane-Butler, cellulose nitrate, diam. 47 mm, pore size 0.45 μm, white grid, sterile, pkg of 400 ea. MicroPlus-21 STL membrane circles white, for Membrane-Butler, cellulose nitrate, diam. 47 mm, pore size 0.45 μm, black grid, sterile, pkg of 400 ea. MicroPlus-21 STL membrane circles white, for Membrane-Butler, cellulose nitrate, diam. 50 mm, pore size 0.45 μm, black grid, sterile, pkg of 400 ea.