五寸釘[gosunkugi] long nail
間釘[aikugi] double-pointed nail
出る釘は打たれる[derukugihautareru] the nail which sticks out gets hammered down (used to encourage conformity)
切り釘[kirikugi] brad
裏釘[urakugi] nail sticking through

装釘[soutei] binding (book)
釘抜き[kuginuki] pincers
金釘流[kanakugiryuu] a scrawl
ねじ釘[nejikugi] screw

閾値[ikichi] threshold (amount, dose, etc.)
識閾[shikiiki] threshold of consciousness
閾下[ikika] subliminal (below the threshold of sensation or consciousness)
閾刺激[ikishigeki] threshold stimulus

検知閾値[kenchiikichi] detection threshold
痛覚閾値[tsuukakuikichi] pain threshold
閾値下[ikichika] subliminal