Note: this filter set does not include a bellow-the-lens filter holder, please be certain your enlarger has one.
This is a 2.5" set of mounted Ilford Multigrade darkroom contrast printing filters. The set is in very good condition. This type is most commonly used below the lens.
Ilford's documentation is highly recommended for beginners and veteran darkroom printers alike: https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/Contrast-control-for-Ilford-Multigrade.pdf