nail down vs pin down

nail down and pin down both are verbs.

Word	Noun	Adjective	Verb	Adverb
nail down	No	No	Yes	No
pin down	No	No	Yes	No

As verbs, nail down and pin down are synonyms defined as:

Other synonyms of nail down include narrow, narrow down, peg down, specify.

nail down (verb)	pin down (verb)
make final; put the last touches on; put into final form	define clearly
define clearly	attach with or as if with a pin
succeed in obtaining a position	place in a confining or embarrassing position