Coolant change; drain plug size questions

[Iroll_]

Good afternoon everyone,
It's been awhile since I have posted, thank you for your consideration.
Would anyone know the correct size of the radiator drain plug, so that I may buy the correct deep well socket or allen key?

thank you in advance,

[hoonk]

would anyone know the correct size of the radiator drain plug

It's a plastic plug and I believe a 3/8 drive 13mm deep works