Estes Apollo Little Joe II Build, Part 17, Fin Support

Here's the final stick size - Your fit may be different. Cut a little large and fit to your model.
The overall length is 2 11/16" with the taper starting 1 5/16" from the end. The tapered end to the right fits into the fin cavity.




The instructions don't mention it but imply the rear centering ring is even with the end of the body tube.
On the actual Little Joe II the nozzle plate was slightly recessed. I could build up the inside so the rear centering ring is closer to the bottom of the tube but will probably leave it as is.
This picture was posted by John Pursley in the TRF build. 

I'll be following John Pursley's advice and make the nozzle plate and centering ring removable. Some flights have shown some melting of the plastic nozzles.

With the rear centering ring against the square fin supports it's a very strong assembly.

Again I can't take credit for using a fin reinforcement spar. The master modeler's at The Rocketry Forum - George Gassaway, James Duffy and John Pursley figured out the structural improvements.

The fins are probably fine without the stick reinforcement. I've read a few launch reports where a fin has been knocked loose from the corrugated wrap on a hard landing. Plastic to plastic bonds between the fin and the body are sometimes a problem.