カチッと

adverb

with a click; with a snap

Describes a short, sharp mechanical sound, like a switch, lock, or lid closing neatly.

• スイッチをカチッと入いれる。

  I flip the switch with a click.

• ふたがカチッと閉しまった。

  The lid snapped shut with a click.

adverb, noun or participle which takes 'suru'

firmly; tightly; precisely

Describes something fitting or being secured exactly in place, often with a sense of neatness or precision. Can be used adverbially or with する.

• 部ぶ品ひんをカチッとはめ込こむ。

  I fit the part firmly into place.

• 引ひき出だしをカチッと閉しめる。

  I shut the drawer tightly.