Allen-Bradley CompactLogix 1769-L23E-QB1B Installation Instructions Manual page 13

CompactLogix Controller 13
4. Close the locking tab on the top of the module.
5. If using another expansion module, complete steps
2...4 for the second module.
6. Align the tongue-and-groove slots of the end cap with those on the right of the packaged
controller or expansion module.
7. Close the locking tab located on the top of the end cap.
Rockwell Automation Publication 1769-IN082C-EN-P - February 2013