Tractate Kelim - Chapter 13 - Mishnah 2 כלים פרק י״ג משנה ב׳

A koligrophon whose spoon has been removed is still susceptible to impurity on account of its teeth. If its teeth have been removed it is still susceptible on account of its spoon. A makhol whose spoon is missing is still susceptible to impurity on account of its point; If its point was missing it is still susceptible on account of its spoon. A stylus whose writing point is missing is still susceptible to impurity on account of its eraser; If its eraser is missing it is susceptible on account of its writing point. A zomalister whose spoon is lost is still susceptible to impurity on account of its fork; If its fork is missing, it is still susceptible on account of its spoon. So too with regard to the prong of a mattock. The minimum size for all these instruments: so that they can perform their usual work.