The term 'pen fillers' refers to substances used to fill the reservoir of a fountain pen. The two crossword solutions for this term are 'INKS' (4 letters) and 'PORKERS' (7 letters). INKS are liquid or paste-like substances that are used to write or draw with a pen. They are usually composed of pigments, dyes, and other chemicals. PORKERS, on the other hand, are solid wax-like substances that are used to fill the reservoir of a fountain pen. They are made from a combination of waxes, oils, and other materials.