fasten
v.v. to close or join two parts of something together so they stay in place. You usually do this with things like buttons, zippers, or seatbelts.
v. to attach, join, or close something firmly using a mechanical device or physical pressure. Transitive — requires a direct object.
Please fasten your seatbelt before the car starts moving.
The hiker stopped to fasten the straps on her backpack to prevent it from shifting during the climb.
Before the storm arrived, the crew worked quickly to fasten the heavy shutters and secure any loose equipment on the deck to prevent wind damage.
From Middle English fastenen, from Old English fæstnian, from Proto-West Germanic *fastinōn (“to secure, fasten”). Equivalent to fast + -en.
The verb is transitive and takes a direct object. It is frequently followed by the preposition 'to' when describing the act of attaching one object to another.
fasten your seatbelt to the bucklefasten your seatbeltFasten is often used alone with the object being closed; adding 'to the buckle' is redundant and sounds unnatural to native speakers.