(1):

(n.) A rough sled or dray used for dragging logs, hauling stone, etc.

(2):

(n.) A weight which is dropped into a bore, as of an oil well, to explode a cartridge previously lowered.

(3):

(n.) A device, as a loosely fitted plug, which is driven through a pipe by the pressure of the contents behind the plug to clear away obstructions.