What are Megerah and Charitzei ha'Barzel?
Rashi (Shmuel II, 12:31): They are matters used to afflict, i.e. a saw with many teeth close to each other and a threshing Kli with many grooves, like "Petzirah Pim 1 " (Shmuel I, 13:21), respectively.
Rashi (13:21): It is a file with many mouths and spikes to sharpen the plow Kelim.
What are Mageros?
Vilna Gaon: They are double saws (i.e. one can cut with either edge of the blade; both have teeth - PF).
Malbim: It is one Kli composed of many saws. In Shmuel II, 12:31 it says Magzeros. 1
Radak (Shmuel II, 12:31): Magzeros are axes used to chop wood.
What is the meaning of "va'Yashar ba'Megerah"?
Radak: He cut them with a saw. Va'Yashar is like "Im Yisgadel ha'Masor Al Menifo" (Yeshayah 10:15).
