Siemens SIMATIC FM 353 Manual page 25

Mechanical transmission elements
These include not only the axis, but also gear trains and clutch systems.
Peripherals
All other additional equipment is covered by the term peripherals.
Peripherals mainly include:
S Limit switches to limit the positioning range (safety devices).
S A programming device (PG) and the "Parameterize FM 353" parameterization
software.
FM 353 Stepper Drive Positioning Module
6ES7 353-1AH01-8BG0
Basic Principles of Positioning
J
2-3