Flip up scope cap

I had been searching for a while for a flip up scope cover for the objective on my sightron 60mm and had looked at the butler creek range. These seem fairly cheap but they make such a wide range of sizes and finding the right size was easier than I thought.
Firstly I looked on the butler creek website and they recommend a #51. I did a bit of googling and others had used a #53 or #53A. I thought something ain't right if there is such a difference in what people are fitting to this scope.
After a bit of pondering I figured I'll just take the sunshade down to my local shop and in a couple of minutes I had a perfect fitting flip up cover for my scope. If your objective outside diameter is 69mm and you're happy enough with a butler creek get the size #54.
Learnings...sometimes you have to pull your head out the computer and take your sh!t to the shop!