Rolex 6534 - which is the right crown size?

[Watchpilot75]

Hi there, I am new to the Rolex Forum´s world. I recently bought an old Rolex 6534 from I 1957 which is missing its crown and needs hence some attention... As I am really (unfortunately) no expert but beginner, I am struggeling to find the right crown reference for the 6534. It looks to me that a 24-600 is needed but I struggle with the additional digit ... the one which is behind the 24-600-x... Anyone who can help me here? Best, Watchpilot75