What is the min and max blade size of a folder you think acceptable to carry?

Regardless of laws, what is the tiniest blade size you’d carry with you in your pocket, not in bags/car/etc. and what is the biggest size you’d consider carrying?

Also, what the min and max size you think is acceptable to be carried in a keychain?

Consider this as the main blade, the one and ony you’d carry all the time…

Please, use metric system and pics are welcome!