Remembering that Annie's battens, though they are 38mm dia, are in the stronger T8 temper, which is hard to get in Australia; and remembering that my 38mm Australian battens, in T5 temper, bent if I sneezed too hard on them, I'm inclined to suggest that if you can only get T5 temper, you should go for 45mm dia, 50mm being a little too big for Redwing.