Always start with the assumption that you have the most common stamps, not the rarest. 594 and 596 are very rare stamps and are perforated 11 x 11. The most common stamp with this design is a 632 that has perfs of 11 x 10.5.
The single stamp you show is clearly a 632, it has perfs 11 x 10.5. Using your image, I have taken the perfs from the left side and compare them against the other three sides. As you can see, the perfs do not align so it cannot be a 594 or 596.
Don
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