metal rod; iron bar; crowbar
General term for a long, solid metal bar, often iron or steel. Can refer to a crowbar or any similar tool.
The burglar pried open the window with a crowbar.
Several thick metal rods were lying at the construction site.
iron club; night watchman's staff
Specifically a traditional iron staff with rings at the top, historically carried by night watchmen. Often appears in the idiom 金棒引き (かなぼうひき, night watchman).
In period dramas, you can hear the sound of a night watchman dragging his iron staff.
The night watchman carried an iron staff as he patrolled the town.