Hey all,
it’s a question of length and number. The Woodworker and Journeyman Y rails are 800 mm long, and there are two of them, so 35 mm rails are strong enough. The X rails on Journeyman and Foreman are 1200 mm long, and there is only one of them, so are 50 mm thick.
Foreman is 1200 x 1200 mm, so both are 50 mm thick.