That dimension you list is for a 1 or 1-1/2 frame.
BUT... earlier 0 frame 20 and 16g guns were also fitted in this size plate. But later guns used the plate that more coincided with an 0 dhbp size. That is under 5” in height.
It depends on what era your gun was made really as to which size is correct.
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B. Dudley
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