Kelim, Chapter Twelve, Mishnah Eight
1) A pen-knife, a writing pen, a plummet, a weight, pressing plates, a measuring-rod, and a measuring-table are susceptible to impurity.
2) All unfinished wooden vessels also are susceptible to impurity, excepting those made of boxwood.
3) Rabbi Judah says: one made of an olive-tree branch is also clean unless it was first heated.
Section one: All of the instruments in this section are metal vessels and are therefore susceptible to impurity. Pressing plates are used in pressing olive.
Section two: Wooden vessels, unlike earthenware ones, are considered susceptible to impurity even if they are not completely finished. This is because they are usable even in their unfinished state. The exception is boxwood, because its bark is thick and vessels made of it are not considered vessels until they are finished.
Section three: Rabbi Judah adds that vessels made of olive-tree branches are not susceptible unless the branches were first heated up to remove their moisture.