BMS School Rocket, Build, Part 3, Engine Mount

From the instructions:

This shows a dry fit, the centering rings aren't glued over the laser cut lines yet.

The Kevlar shock cord is tied through a cut hole and around the engine block.

I prefer tying a small loop knot and setting that under the top bend of the engine hook. This is an idea from Semroc. 

More later - 

OOPS! Originally I raised the lower centering ring above the laser cut positioning line to give more flex of the engine hook. I had to lower the ring, it would be in the way of the TTW fin tab.

I set the rings in a light ring of glue, applied to the tube. The ring is slid into the glue ring.

Side by side, 

Here's how the engine mount centering rings set when glued onto the laser cut lines.

You have some good space around the rings and fin tabs.