a sole or a ruler for measuring shoes, or something of that sort
Alonso de Molina:
cacuapalli. suela o norma de zapato, o cosa semejante. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 11r. col. 2. Thanks to Joe Campbell for providing the transcription.