Mohs Hardness Testing Pencils: 3-9 of the Mohs Scale of Hardness. Mohs minerals are set inside brass holders and bonded to a wooden handle, numbers 3 & 4 are manufactured from metal alloys with a hardness that corresponds to the scale. The set is supplied in a protective canvas roll, ideal for use in field or laboratory. Instructions included. Dimensions: 26cm x 18cm. Pencils are 12cm long.