[russdill]

Lots of rocket components look like gears. The outside skin of the rocket often had internal vertical stringers and so components need cutouts that end up looking a bit like gears

[jamieplex]

true, but I guess I have never heard of an 8' diameter rocket before...

[schiffern]

SpaceX notwithstanding, it's pretty common for orbital rockets to "neck down" for upper stages.