The bolts are part of the Common Berthing Mechanism (CBM).
The Common Berthing Mechanism (CBM) is a complex collection of
latches, bolts, Ready to Latch (RTL) indicators ... and computers to
control this equipment. This system can be operated by either the
ground or the crew; extravehicular activities (EVAs) (i.e.,
spacewalks) are not required to use this mechanism, unlike some of the
truss attachment systems. Once a new module is close enough to the ISS
(RTL), four latches on the ISS side (usually a Node module) are used
to reach out and “grab” the incoming module and pull it closer.
Alignment guides ensure the bolts and nuts of the mechanism are in
line with each other. Once the latches have pulled the two halves
together, bolts on the active CBM are extended into nuts on the
passive CBM. Each of the 16 bolts has a preload of approximately 90 kN
(20,230 lbs) of force on it after the bolting sequence is complete.
This diagram shows one of the four controller panel assemblies with its four associated bolts and one associated latch.
The CBMs are normally operated by the crew. The Personal Computer System (PCS) (aka ISS laptop) display used to control and monitor the CBMs is shown here.
The bolting stages are described here
Bolting is conducted in several stages. The first stage acquires all 16 bolts and their mating nuts and torques
them to an “acquire bolt preload” of 1500 pounds (as measured
by strain gages within the bolts, and monitored by the CBM Bolt
Controllers). After the preload torque is complete, further torquing is discontinued so that temperatures between
the passive ring and active ring can equalize. Once the
temperatures are equalized,the torquing operation resumes. Bolts are commanded, in-groups of four, through several more
torquing stages, proceeding from the initial preload of 1500
pounds up to a final load of 19,300pounds per bolt. The module
is then in its fully berthed position.
Here is a picture of the bolt actuator and a schematic showing a "ready to bolt" bolt.
For further reading: the document below "The Common Berthing Mechanism for ISS" is recommended.