This is a dual-texture, two-sided eraser typically aimed at general use. It sells for about $3.
The two sides — sand and rubber — are designed to be used for pens and pencils respectively. The sand side has a grit to it which will wear down paper that has ink in it where the rubber side is meant the remove graphite which is on the paper (as opposed to sunk in).\
The sand side of the eraser can be very rough on paper so it’s best used lightly. It works better with ballpoint and oil-based inks which tend to sit on top of paper than it does with water-based inks, like rollerballs, or pigment-based fountain pen inks.
The eraser measures 8 x 16 x 67 mm and weighs 12 grams. The eraser is model number 510A.
Tombow Mono Sand and Rubber Eraser Information