I realize that 36mm, 38mm (most common), and 40mm piston sizes were used for the rear calipers on the 700 series.

I am told and the FAQ agrees that the piston size is stamped on the outside of the caliper.

The only numbers stamped in the center of the outside of the caliper that I can find are a "2" on the left caliper and a "5" on the right caliper.

Granted, I am changing both so as long as I use the same size on both sides there should not be an issue but this is driving me nuts not knowing what the original size came with the car from the factory.
Do the "2" and "5" represent the size?
Or am I missing where the stamp is?

There is no boss area with a stamp on my calipers like the photo in the FAQ.

Thank you for any ideas.
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'60 544, '68 220S, '70 145S, '72 144E, '86 745T