A video of this procedure is available at YouTube: https://www.youtube.com/playlist?list=PLYV5R7hVcs- 
CTkyVDu-5Lhy1r9G-4PQGl
.
Procedure
Step 1.  Loosen the two thumbscrews located on the front of the server to disengage it from the rack. 
Rack front
Figure 17. Disengaging server from the rack
1
Latches
2
Thumbscrew
Step 2.  Hold the mounting ears on the front of the server; then, slide the server all the way out until it stops. 
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ThinkSystem SR645 V3 User Guide