The Grand Seiko SBGW231 is very similar to Patek philippe Calatrava 5196G, same 37mm, albeit with the central second instead of sub-second. Particularly the very nice creamy, yellowish egg shell dial...which not only give stroing vintage look, but also provide good contrast with hands and markers, f
I know the width is 18 mm, but i don't know the part number. Many seller in Ebay sell this link, but they don't mention the part number. So i'm afraid it does not fit, although the width is same. If somebody can inform me, would be thankful. I have emailed IWC but no answer.