Estes Hex-3, #7263, Build, Part 2, Engine Mount

I like to sand the centering ring ends flat. From the manufacturer, the edges are cut at a slight angle. 

TIP: If you ever build a kit where the rear centering ring is seen, even with the end of the main airframe tube, you'll want them flat. The finished look will be cleaner.

The wrap around marking guide fits! A perfect match.

After you mark and extend the the pencil lines down the tube,

set the tube on the large base plate to get an idea how it fits.

The split ring usually goes on the bottom of the engine mount. The open split allows movement of the engine hook.

On the left side picture, I used some masking tape to hold the split closed until the glue dries.

On this model, the open ring allows passage of the launch rod.

On the right side you can see the top edge of the launch lug through the open slot. 

Here's the finished engine mount - 

The low end of the launch lug rests against the Mylar retention ring. The upper end of the lug is cut to sit under the upper ring.