what is the internal diameter of the red threaded end of the assembly? Is it the same as the internal diameter of the threaded 2L bottle opening?

This answer is coming from Dallas Murdoch, Owner of EZ-Launch LLC and a dealer for the red fins. The internal portion of the top half of the red fin assembly is threaded and screws onto the launch bottle. Its diameter is 29.6 mm. The internal diameter of the threaded opening on a two liter launch bottle is 21.0 mm. The internal diameter of the lower 1/2 of the fin assembly is 21.3 mm. The internal diameter of the pop bottle where the external threads are located is 21.1 mm. If you are using an EZ-Launch bottle rocket launcher with the red booster fins, you need to have a round white ABS plastic insert glued to the lower threaded portion of the red booster fins. This comes with the booster fins when ordered from EZ-launch.com and is necessary to lock the bottle with the fins into the EZ-Launch bottle rocket launcher. Also, The red booster fin assembly requires a separate black launch pipe in order for the bottle to maintain a steady air pressure and hold the water inside of the bottle. This also is included in the EZ-Launch bottle rocket booster kit that comes from EZ-Launch LLC.

Why do these required using an additional nose cone?

the additional nose cone improves aerodynamics and is where the parachute is placed for launch

What type of plastic is this product made with, my son has sensitivities.

The StratoFins are made from polypropylene (PP), which is the same plastic on the white cover of a Tic Tac Mint container that has the "living hinge."

Like the nose cone idea. Anybody use a mylar parachute?

We have no experience with using mylar for a parachute, but that sounds like an interesting idea. It should be durable and lightweight, which might make a great choice for material. The only issue might be how well it drapes, since it could be somewhat stiff although you could pre-wrinkle it. Plastic trash bag work for parachutes and mylar wouldn't be too much different from that of than draping. We use rip-stop nylon for our parachutes, which is very durable with great longevity. If you are using it on a water rocket, watch the video link if you haven't seen it already. It will help explain attaching it to a 2-liter soda bottle and offer deployment techniques.

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StratoFins Screw-on Water Rocket Fins

Product ID: 327415288

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📏Fits 2L soda bottles & smaller

🔩Screw-on, no tools/glue

🚀95% launcher compatibility

Description

🚀 Elevate your water rocket game—launch higher, fly straighter, and own the sky!

STEM READY FUN - Perfect for science projects, parties, or solo experiments—ignite curiosity and impress your crew.
EFFORTLESS ASSEMBLY - Screw-on design means zero tools or glue needed—get your rocket flight-ready in minutes.
COMPLETE KIT INCLUDED - Everything you need—3 fins, attachment ring, and detailed instructions for next-level launches.
UNIVERSAL LAUNCHER FIT - Works seamlessly with 95% of all launchers, homemade or commercial—no limits to your launch setup.
PRECISION FLIGHT CONTROL - Durable plastic fins ensure straight, stable flights—say goodbye to tumbling rockets.

StratoFins are durable, screw-on water rocket fins compatible with 95% of launchers, designed for 2-liter soda bottles or smaller. The kit includes 3 fins, an attachment ring, and instructions, enabling quick, tool-free assembly. Engineered to stabilize flight and prevent tumbling, StratoFins enhance STEM learning and outdoor fun for ages 14 and up.

Specifications

Product Dimensions	19.05 x 13 x 4.45 cm; 28.35 g
Manufacturer recommended age	14 years and up
Item model number	FIN-1
Educational Objective(s)	STEM
Language:	English
Number of Game Players	1
Number of Puzzle Pieces	4
Assembly Required	Yes
Batteries Required?	No
Batteries Included?	No
Material Type(s)	Plastic
Color	Red
ASIN	B00BA3K0WY

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