#54740, "RE: Titanic teak top rail " In response to Reply # 0
The size of the top rail varied depending on its location. The rail shown in your photo ('A' deck aft) was 3 inches high by 6 inches wide according to 'Titanic: The Ship Magnificent'. The cross-section, as best I can judge from photos, was as shown here.
#54778, "RE: Titanic teak top rail " In response to Reply # 1
I found a construction photo of Olympic showing the railing partly built, and the top rail cross-section can be seen. It seems to be a bit flatter on the bottom than the top, so I've drawn a couple of shapes that might correspond better to what's visible in the photo.