The numbers 24/24 and 26/26 refer to the width of your Panerai strap at the case lugs and the buckle in millimeters (mm). The first number is the case lug width and the second is the buckle width.
If you are unsure about your Panerai's watch strap width, please feel free to contact LussoStraps at info@lussostraps.com with your model number and we will happy to advise.
The numbers 125/75, for example, refer to the lengths of the two pieces of the strap in mm. The first number is the length of the longer side with the holes, and the second is the length of the shorter buckle side.