NOS nylon ball cradle cap.
This attaches to the bell armature / plunger on the VUK with a roll pin.
If your VUK is inconsistent in pushing the ball up, examine this cup/cradle; it has 4 fingers on it.
I have seen many with 1 or 2 broken, the result, the ball will not be positioned correctly for the up-kick, and may, or will hit the sides of the wireform, loosing inertia prior to the apex, resulting in repeated attempts.
It is used on many titles.
This will work only fit a Data East / Sega, if you drill the neck cavity thinner, which will allow it to fit over the thicker nylon tip; or change the VUK plunger to a Williams.
Williams / Bally: 03-8053