1)
What is "ha'Barzel"?
1.
Rashi: It is a saw.
2.
It is the iron blade 1 (without the handle - Radak 6). (PF)
1
Radak did not specify what Kli it was. "Va'Yigzeru" (they cut) suggests that it was a saw, like Rashi writes; an ax is used to chop. However, below (6) Radak says that the wood entered the hole in the blade. This applies to an ax; I did not find any Meforshim discuss a hole in the blade of a saw. (PF)
2)
Why does it say "v'Es [ha'Barzel]"?
1.
Radak: The beam [that he was cutting] fell with the blade 1 .
1
Why does the verse hint to this? (PF)
3)
Why was he troubled because it was borrowed?