Honeywell RTH7400D Owner's Manual page 56

4. Align the screw blocks with the pins on the back of
the thermostat.
WALLPLATE
5. Push the thermostat straight onto the wallplate until
it snaps into place.
69-1726—1
Replace Batteries (Cont)
TERMINAL SCREW BLOCK
56
PINS ON
BACK OF
THERMOSTAT
M22299