The narrower mid-body is glued together. There are no internal supports, it's a hollow square tube.
This is the dry fit of the three sections. Everything slip fits very well.
You can see the laser cut geometric design swirls over the side walls. I can't see how to finish these, sanding the parts square just about removes them. If I didn't sand everything smooth, they'd probably show up in a color coat.
This is the Teflon engine lock ring in place.
An 18mm engine slips in easily. The ring tabs go into their four slots and the ring is turned to hold the engine in place.
Pretty ingenious, as long as you don't lose the ring.