A similar hu with cover is illustrated by J. So, Eastern Zhou Ritual Bronzes from the Arthur M. Sackler Collections, The Arthur M. Sackler Foundation, 1995, vol. III, no. 44, where the author, p. 257, describes how the motifs "were first cast in copper, then inserted into the mold and held in place with spacers".
See, also, the closely related hu of the same size, sold in these rooms, 21 March 2002, lot 70.