Here is what we have so far. I also assigned a nice default Blinn shader to it so we no longer see the red areas (Fig.25).
Step 5: Connecting parts together
First we merge the two halves of the middle part together. Simply combine and merge them.
Now it is time to connect the middle part to the bottom and merge them together. As we saw earlier in this tutorial, the number of subdivisions differed for both the middle and bottom parts. To fix this problem, we add some new edge loops to the middle part to match the edges of bottom and then we simply delete all the old edges that don't match (Fig.26 & Fig.27).
Once you are done, merge all the vertices together and extrude the middle towards the inside where the middle and bottom part are connected. Call the new object "Bottle" (Fig.28).
Step 6: Adding extra details to middle part
In this step, we are going to add more definition to the middle part. Simply, move the vertices and extrude their faces to make a basic slot. In this model we need to have four slots (Fig.29).
Step 7: Combining parts
This is a simple step. Combine all the objects except the cap's treads and call it "Coca_Bottle" or whatever you like. The reason we don't combine the treads with the rest of objects is that once we apply mesh smooth to them they get rounded and that is not something we want. Also, make sure you delete the history of all of the objects before combining them.
if you feel the bottle needs to be a bit fatter, make sure you hold "Ctrl" while scaling the object on the "Y" axis. This way you are scaling the object on both the "X" and "Z" axis simultaneously.
Here is the final model after applying mesh smooth. At this stage we are done with the modeling part (Fig.30).