On 18th Dynasty Egyptian cubits the 20th finger is labeled a remen. The 16th finger is indicated as being a "t'eser" and the hieroglyphic symbol on the 15th and 16th fingers is similar to the remen but overlaps the border between them. The glyph appears to be that of a forearm with the hand grasping a rod which can be seen more clearly on the cubit at the Museo Egizio in Turin, Italy. There is a picture of this cubit stick in Mathematics and Measurement by O. A. W. Dilke on p. 23.
Mathematics in the Time of the Pharoahs by R. Gillings p.220
If one does an actual measurement one does get a value very close to a foot. If you want to check this measurement I would recommend an assistant since balancing the tape measure while taking a picture is rather difficult.