/lib/udev/rules.d/60-mt-st.rules is in mt-st 1.3-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # Use stinit to set default parameters on st device creation
KERNEL=="st[0-9]", RUN+="/sbin/stinit %n"
KERNEL=="st[0-9]*[0-9]", RUN+="/sbin/stinit %n"
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