Sad to see Mark retire, but I'm sure it's well-deserved!
I have Mark's grates in pretty much everything:
Our family's 18" kettle, our Go Anywhere, both 14.5" WSMs, and our WSK E6.
Mark even took the time to have me measure the WSM middle sections as he told me he has encountered some variation in the size of the middle sections during manufacturing, and he offered two different sizes for the 14.5 WSM top grate depending on the actual diameter of the middle sections.