Many threads here on TRF discussing filling body tube spirals. Previously I’ve used Elmer’s Carpenters Wood Filler (CWF) and Bondo Glazing and Spot Putty (Bondo). I had two full lengths of 38mm Blue Tube and a full length of 38mm Blue Tube coupler in my rocketry parts stash and decided to do a little test. I used CWF thinned to a mustard-like consistency on one, Bondo on another, and finally BSI 30 min epoxy on the last. Normally I don’t fill spirals on couplers, but did for the sake of this activity. Both the CWF and Bondo could be done in one sitting. This is the first time I have tried any type of epoxy to fill spirals and did it in two sittings to keep from making a mess with drips (layed tube horizontal and did top half one day, flipped and did the other half the next day). After drying, all tubes were rough sanded with 100 grit to get the major overfill off, then 220 and finally 400 to smooth them out completely. Immediately after this sanding process I could feel a slight indentation on the spirals filled with the Bondo. For a perfect finish, I would definitely need to do another coat of Bondo and/or use multiple coats and sanding with a filler/primer. I have done this previously. With the CWF I could also feel a slight indent with my fingernail. It was not as pronounced as the Bondo, but still noticeable. The epoxy filled spirals were perfect in my estimation. Could not feel any texture change going over the spirals, and I tried hard to find some. So, all these tubes are still sitting around a few weeks later. I took a good look and feel of them again today. The Bondo has shrunk/contracted a little more and the indentations are even more pronounced. The CWF seems about the same. Epoxy still great. With two prior builds using the Bondo method, even after a second Bondo coat then priming and painting I have had visible spirals seem to show up several months later. Note sure if anyone else has seen this. I do live in a very low humidity region (Colorado) and wonder if this effect is pronounced because of that. In terms of application, the Bondo took the least amount of time and effort. Right out of the tube and rubbed into the spiral. CWF was second easiest. After thinning, ‘paint’ along the spirals. As I mentioned, the epoxy took two sittings and was the slowest to apply. I used a bambo kabob skewer to drag it into the spiral. However, given the results, this will be my new favorite method.