Dell Precision T3400 (Late 2007) - Manual (Page 161)

Adding and Replacing Parts
161
4 Align the notch on the bottom of the memory module with the crossbar in
the memory module connector.
1 memory module connector
(DIMM_1) 2 securing clips (2)
3 memory module connector
1 cutouts (2) 2 memory module
3 notch 4 crossbar
2
3
1
3
2
1
4