The 7548/7546 are both 27mm diameter and 4.6mm thick:
http://www.thewatchsite.com/d1/files/Seiko Technical Manuals/7548A.pdf
http://www.thewatchsite.com/d1/files/Seiko Technical Manuals/7546A.pdf
http://www.thewatchsite.com/d1/files/Seiko Technical Manuals/7548A.pdf
http://www.thewatchsite.com/d1/files/Seiko Technical Manuals/7546A.pdf