Rapier of the needle doesn't seem to give bonus crit chance
According to great identify, the rapier of the needle is "very good at scoring critical hits in melee". Tested on a blessed character with 100 find weakness and no other relevant intrinsics. With unarmed attacks I got 50 crits out of 200 hits. With rapier of the needle I got 52 crits out of 200 hits. The rapier seems to be giving either an insignificant crit chance bonus, or none at all.