I first flew back in the 1940s as a four or five year old. I have a vague memory of a seat belt locked with a wooden peg inserted into a webbing loop. The aircraft was probably a Vickers Viking, a very unreliable aircraft.
We landed at Lyon, France, no wheels on the grass and we have a photograph of the crew and passengers in front of the downed aircraft in a field! Was there ever such a seat belt?