If your asking the nib size as to writing tip most of the kit or component nibs are what I would call a heavy medium, if your referring to the physical size as Smitty said there are two sizes that come with our component sets 5 MM and 6MM to tell which size your component sets have 5mm or 6mm measure the width of the feed , they will measure 5MM at the widest on the smallest fountain pen components and 6MM on the larger component sets. Cleaning is pretty straight forward,
As I said it's not rocket science to clean, go to the infant dept. at your local Wal-Mart and purchase a nasal syringe, fill a small bowl with tepid water, have an empty small bowl next to the one with the water. Run water (tepid water) over your feed and nib from the back side until it runs fairly clean , sorry I should have told you first to remove the section and take the cartridge or pump of first, Now fill your syringe with the tepid water and place it on the back side of the feed where the cartridge or pump attach and flush the feed into the empty bowl, you'll see ink still coming out do this as many times until it runs clean. You now have a clean feed,nib and housing.