I wonder if the Speedmaster Date Strap, 323.32.40.40.04.001 (19mm Cordura strap) the would fit on the Speedmaster Racing, 326.30.40.50.06.001? How about the Aqua Terra 38.5mm? Thank you for your answer.

 

If the lug width is the same I don't see why not.

 

I think you are right about SM Date and SM Racing strap should be interchangeable. The AT 38.5mm uses 19mm strap. I wonder if this 19mm Cordura strap would fit?