"I ordered a set of snaps at the 10mm size, based on the diagram which indicates that the button itself would be 10mm. They are not; they are actually more like 8mm, and the outside casing is 10mm.
This aside, they arrived quickly, the tool kit made installing them quite easy, and there were enough that I could substitute rather than supplement the buttons I had originally planned to use.
I would perhaps suggest that the diagram be updated to ensure the measurements are correct, and that the size selection indicates which component you are referring to when you choose a size."
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