This is a replacement wrist body for the Heathkit Hero Robot's arm. The two halves have the correct cutouts and slots to hold the original motors and bearings, except for the connection to the wrist pivot motor. On my robot, the wrist body was broken and that connector piece had long since been lost.
For the pivot motor connection, this design holds a 3 mm flange shaft coupling such as this one: https://www.aliexpress.com/item/3mm-Flange-Shaft-Coupling-Steel-Rigid-Flange-Plate-Shaft-Connector-Optical-Axis-Support-Fixed-Seat/32874445570.html
Use two small plastic screws to prevent the coupling from rotating -- only install screws in the two holes nearest the stops in the body, otherwise the post on the fixed portion of the wrist will run into the screw heads.
One of the four #4-40 screws that hold the body together can be reused, the other three must be replaced with longer ones and fastened with nuts in the other half of the wrist body.