 This ballpoint is first vitrified by heat, then ground down and milled to an accuracy of between spinning plates coated with industrial diamond abrasives.Since 1991 the pen's streamlined polypropylene cap has had a small hole to reduce the risk of suffocation if the cap is inhaled.Polypropylene is used instead of polystyrene because it absorbs impact better, reducing the chance of the pen cracking or splitting if it is dropped onto the cap.