base section

基本解释

The total beam and semi-beam are connected into cross beam with pin , and connect with base section.
整梁，半梁由销轴连接成十字架，与基础节相连。
Furthermore the burner membrane uninterruptedly flows over from the base section through the transition region into the closing section.
并且燃烧室膜片是无间断地由底部段通过过渡段进入封闭段。
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The shape of the membrane is such that the smallest radius of curvature of the transition zone is smaller than the smallest radius of curvature of the base section.
燃烧室膜片的形状是这样的，使过渡区的最小曲率半径小于底部段的最小曲率半径。
ip.com

However, in this case, the three lenses have color detail around them which makes them look anything but sinister, and the circular base section might look a little large, but in fact it's light in the hand -- and actually helps it sit quite comfortably atop a helmet.
ENGADGET