BASON, in mechanics, a term used by glass-grinders for a dish of copper, iron, &c. in which they grind convex glasses, as concave ones are formed on spheres: And by hatters for a round iron mould, in which they form the matter of their hats; and also for a leaden one for the brims of hats, having an aperture in the middle, of a diameter sufficient for the largest block to go through.