Black hard plastic with metal clip on top. Size of a standard pen. Removable cap and base that unscrews. Inside base there is a white very light kind of foamy eraser material.

Ballpoint pen my.pen black/white - Herlitz

Mechanical Fastening - ScienceDirect

A sfera, Penne, Collezionismo - PicClick IT

Boost your Brands by amp-mp - Issuu

Black Plastic Cap with F217 Liner - 24/414 CT

Parker, Fountain Pens, Pens, Pens & Writing Equipment, Collectables - PicClick UK

Do you prefer flat-ended or round-ended fountain pens? Why? : r/fountainpens

Eraser Pen

picks - Zipf Lock Company