The Build Guide fits fiberglass and paper sized body tubes. Easily the most useful tool to ensure everything is aligned and in place. It serves 3 crucial functions in your build: 
 
Fin Alignment - You don't need large expensive tools that look like they came out of the middle ages to get straight and square fins every time you build your kit. Slide the Build Guide onto your body tube, secure your fins in each fin guide slot and you are done. No need to keep the rocket vertical while things cure and dry either. Since the Fin Guide is so small, you can put your rocket on your rocket stand and continue working on other aspects of the kit while the fins cure. This is the easiest and fastest way to align your fins - even easier than “Just eyeballing it”! 
 
Tube Marking - With this guide, you will get a perfectly straight and square line to mark around the tube for cut lines and minimum diameter fin placement. Place the end of the guide where you want to mark the tube and draw around it. Done! Additionally, mark center lines with precision. Each side has a notch at the front that is centered between the two fins. Mark where the notch is then use that to draw a line up your rocket. Now you know anything placed on that line is perfectly centered. 
 
Drill Guide - Combined with your tube markings, you will have center drilled holes every single time. With the Build Guide, your rail button holes and vent holes will not only be centered on the line but also always perpendicular to the body. To top it off, your drill bit will not skip or walk along the body tube as your drill! 
 
There are three sizes of drill guides: 1/16in, 3/32in, 1/8in. 
 
Technical details: These guides are modeled off Mach 1 fiberglass tubing. The size of the tubes these were made to fit are below. These are meant to fit snug against the tube. Please make sure your tube is within 1mm of the sizes below. 
 
Body Tube Sizes: BT20 = 19.0 mm | BT50 = 25.0 mm | BT55 = 34.2 mm | BT60 = 41.0 mm | 2.2" = 57 mm | 2.6" = 68 mm | 3" = 78.75 mm | 4"=101.6 mm | 5"=127 mm