Lexmark MS911 Service Manual page 660

The motor (staple unit) controls the stapling. The sheets are positioned under the clincher staple arm, which clamps
the sheets to hold them in place during stapling. If the number of sheets to be stapled exceeds the limit, then the stack
is fed to the bin without being stapled.
# Part
1 Sensor (SHPF staple unit carriage home)
2 Motor (SHPF staple unit carriage)
3 Sensor (SHPF staple unit carriage center)
4 Staple unit
# Part
1 Staple cartridge
2 Motor (staple unit)
3 Staple
4 Paper stack
5 Staple arm
Appendix C: Theory of operation
660
4021, 7421