Комментарий к Бамидбар 35:16

ואם בכלי ברזל הכהו BUT IF HE SMOTE HIM WITH AN INSTRUMENT OF IRON — This is not speaking of one who kills inadvertently, who is mentioned near this (in the preceding verse), but of one who kills intentionally; and its purpose is to teach us that with whatever instrument one kills, it is necessary that it must have a size sufficient to cause death, because in the case of all of them (vv. 17, 18) it is said, אשר ימות “[an instrument] by which one may die”, the Hebrew of which we translate in the Targum by, “[an instrument] which is of such a size that one may die through it” — in the case of all, except in that of iron, because it is manifest and known to the Holy One, blessed be He, that iron kills whatever size it may be (however small it is), even a needle. Therefore the Torah does not assign a size to it by writing ,אשר ימות בה (Sifrei Bamidbar 160:3; Sanhedrin 76b). And if you say that Scripture is speaking of one who kills inadvertently, — but surely it says lower down, (v. 23) “Or with any stone, even though one may die by it, (even though it is large enough to kill him) seeing him not”, which certainly is by inadvertence. This proves as regards the cases mentioned before it, that Scripture is speaking of one who kills intentionally.

ואם בכלי ברזל הכהו וימות רוצח הוא, “If he had struck him with an iron implement and he died, he is a murderer.” The Torah legislated that if someone killed with a stone or a wooden implement the court will examine if the force used was sufficient to result in death under normal circumstances, i.e. if the victim were healthy. We know this from verse 17: “If he struck him with a hand-sized stone which is sufficiently large to cause death, or with a wooden implement.” These words mean that the court must weigh the relative strength of the blow according to the physique of who administered it and according to the implement employed to strike the victim with. When the blow was struck with an iron tool or weapon, the Torah does not apply such criteria but assumes that anyone who strikes a blow with such an instrument has murderous intentions. Iron instruments, even if as small as a needle are capable of causing death. (Compare Maimonides Hilchot Rotzeach Nefesh 3,1; 3,2, etc.)
If the killer pushed the victim so that he fell off the roof of a building and died, this is a situation covered by the words in verse 20: “if he pushed him out of hatred or hurled him from an ambush so that he died,” the killer is automatically assumed to have had murderous intent. If less lethal instruments caused the death of the victim the court has to assess if the blows inflicted were prompted by hostility. This is why the Torah wrote: “or he struck him in enmity with his hand.”

Of a size capable. כמיסת means “of a size.”