You'll never see a pig in one (4)
I believe the answer is:
poke
'pig in one' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for poke that I've seen before include "Ridicule - . . . . fun at" , "Prod with a sharp object" , "Thrust forward; sack" , "bag" , "Jab or prod" .)