I have several diamond A blocks and each one has really pronounced seams, casting lines and marks. The standard A blocks I have are a much smoother casting. Not sure if it was because the diamond was more often used in an industrial type application and not finished as smoothly or if the casting process was somehow different on the diamond blocks. Just my experience but what I have seen the diamond blocks are like that. I actually used a little jb weld to smooth out some of the flaws on the diamond I just had rebuilt.