Number 7.

Incorrect!

A 2 X 4 sawn (ie. rough cut) is 2 inches by 4 inches exactly

A 2 X 4 PAR (planed all round) is one and seven eighths inches by three and seven eighths inches.

The latter, (in timber lists in the UK at least) is normally listed as Ex 2 X 4, indicting the original from which it was planed.

Anything that measures less is either very heavy handed planing, or a special order size.

Don T.(Ex Joiner and Cabinet Maker)