Hey Mark,

I noticed the page for the ThunderRoc shows the the original rocket was 1.2" in diameter. Not sure where that value came from; it would be between ST-11 and ST-13 (I'm not aware of anything ever being released in ST-12).

Regardless, ThunderRoc used an ST-16/BT-60 tube, which has a diameter of 1.637". It was one of the Centuri releases that used predominantly Estes parts after the merger (Nose cone is PNC-60AH). ThunderRoc appeared in the Centuri catalogs from 1980-83, but '82 is the easiest to read on available online material. I've also provided a link to the instructions from JimZ's site.

http://www.ninfinger.org/rockets/nostalgia/82cen16.html
https://estesrockets.com/wp-content...982_Catalog.pdf
http://www.spacemodeling.org/jimz/centuri/cen5340.pdf

All three of these sources list the T-Roc's diameter as 1.64".

Hope this is helpful!