This 4 cent variant was designed, but never issued.
RU11a, Old Paper
RU11b, Experimental Silk Paper
RU11c, Silk Paper
5 Cent Stamp: RU11a, RU11b, RU11c
Die Approved May 2nd, 1865
First Issued July 1865
Last Issued March 1874
Materials: Old Paper, Experimental Silk Paper, Silk Paper
5,500,408 Old Paper Issued
2,616,192 Silk Paper Issued
Toppan, George L., et al. An Historical Reference List of the Revenue Stamps of the United States: Including the Private Die Proprietary Stamps. Castenholz, 1990.
SCARLETT, Oscar. A Complete Cyclopædia of All the United States Revenue Stamps: Including Document, Match, Medicine ... and Other Tax or Revenue Stamps. William E. Scarlett, 1893.