Any
stage rigger worth their salt will tell you that a
head block is a specialized form of of a
mule block, which is a specialized form of a
sheave.
Actually the head block is a series of sheaves. Located at the top of the grid directly above the arbor for its respective lineset, the head block is where all of the wire rope cables that support the batten are gathered and redirected down towards the arbor.
See the note in mule block regarding the safety and maintenance of this critical part of the counterweight fly system.
Part of the Stage Rigging Metanode