Definitions for joint, butt
The Standard Electrical Dictionary
A joint in belting or in wire in which the ends to be joined are cut off square across, placed in contact and secured. It ensures even running when used in belting. Any irregularity in thickness of a belt affects the speed of the driven pulley. As dynamos are generally driven by belts, and it is important to drive them at an even speed to prevent variations in the electro-motive force, butt joints should be used on belting for them, unless a very perfect lap joint is made, which does not affect either the thickness or the stiffness of the belt. When a butt joint is used in wire a sleeve may be used to receive the abutting ends, which may be secured therein by soldering. This species of joint has been used on lightning rods and may more properly be termed a sleeve joint.