It is a single 7-inch block that is suspended from an eyebolt at the yardarm.Longridge, C.N. & Bowness, E. (1981). The Anatomy of Nelson's Ships. Naval Institute Press. 250. It is the preferred term for the "studdingsail halliard block".Harland, J.H. & Myers, M. (1984). Seamanship in the Age of Sail: An Account of the Shiphandling of the Sailing Man-of-War, 1600-1860, based on contemporary sources Naval Institute Press. 163.
