HPE ProLiant ML110 Gen11 User Manual page 80

d. Retract and hold the front retention bracket.
e. Insert the pins on the mounting flange into the rack column holes.
f. Release the front retention bracket.
5. Slide the server tray into the rack.
The rack rails will click and lock into place when the tray is properly engaged.
HPE ProLiant ML110 Gen11 Server User Guide 80