Meaning of “the bolts that held his face together”

What does “bolts” mean here?

I used to crouch down into the seat and hold my coat in front of my face when I sensed a frightening scene coming, peeking through the buttonhole to find out when it was over. Through the buttonhole Frankenstein’s monster glowered; lightning flashed; sweat poured over the bolts that held his face together.

From the short story “The Movie House” written by John Updike

Solution 1:

This is clearly a description of Frankenstein's monster or something similar. A bolt is a parallel-sided screw that is usually held in place by a nut.

Solution 2:

The second definition at Lexico is:

A long pin with a head that screws into a nut, used to fasten things together.