Meaning of 鎹 in Japanese

Definition of 鎹

かすがい(kasugai) 【鎹】

こはかすがい(kohakasugai) 【子は鎹】

(exp) children are a bond between husband and wife
最近、周りでも離婚が多いようだけど、子は鎹って事は、今は昔となったのかね。
Lately I see a lot of parents getting divorced. I wonder if the idea of kids being a bond between their parents is just a thing of the past.

とうふにかすがい(toufunikasugai) 【豆腐に鎹 ·豆腐にかすがい】