(Nomi to ieba tsuchi;
“When [asked for] a chisel, [one also brings a] mallet”)
To be intelligent and thoughtful in all things – as a description, or as an imperative. If someone asks you to bring them a chisel, having enough consideration and foresight to also bring a mallet, since they’re used together.
We begin with the noun 鑿 (nomi), “chisel,” marked with the particle と (to). The particle here acts as speech marker, as demonstrated by the following verb 言う (iu), “to say,” here in perfective form and taking the conditional suffix ば (ba), “when.” Without further particles or verbs, the result of the condition is reduced to simply the noun 槌 (tsuchi), “mallet.”
This is the の (no) entry of the Kyoto iroha karuta set.
There are several variants on the phrase, including one that specifies a 才槌 (saidzuchi), a small mallet. Compare and contrast 一を聞いて十を知る, which includes the same powers of insight but leaves out the implications of consideration for others.
(“Gendai shakai de wa hotondo no koyoushu ga nomi to ieba tsuchi to iu kidzukai ga dekiru hatarakite wo sagashiteiru ga, sono hatarakiburi ni fusawashii kyuuryou wo haratteiru ka wa betsu no hanashi da.”)
[“Most employers in our contemporary society are looking for workers who take that extra step. Whether they’re offering wages commensurate with that level of diligence is another story.”]