The part of the taper shank drill which fits into the slot of the drilling machine spindle is called as Tang
Least Count is the smallest value, which an instrument can measure is called least count of the instrument. Example: least count of Engineer's steel rule is .0.5 mm.
Toughness:
When a huge external force is applied on a metal, the metal will experience fracture. Toughness is the ability of a metal to resist fracture. The ability of a material to resist fracture due to high impact loads, is called toughness.
Brittleness
Brittleness is a property of material which breaks with little or no deformation.
Ductility:
Ductility is the property by which a metal can be drawn into thin wires. It is determined by percentage elongation and percentage reduction in area of a metal.
Hardness:
Hardness is the ability of a metal to resist permanent change of shape caused by an external force.