To begin, you need this stuff:
PETG
1/2” Brass
17/32” brass (optional)
Lighter or hairdryer

Nest the 1/2” brass in the PETG. Use the 17/32” brass if you want to keep part of the PETG at it's original dimensions.

Heat a section of the PETG with the lighter. This works best if you rotate the tubing quickly and keep the section between 1-2 inches.

Pull (yes, pull) the two ends of the PETG apart. This stretches the tubing and shapes the ID to fit the OD of the 1/2” brass, giving the PETG a similar ID to 17/32” brass. The 17/32” brass keeps that section of the tubing at a 17/32 ID, or normal ID.
Move along, and do the same to the rest of the tubing.

This is really easy to do, and has a great fit for darts. Unlike the spring method, the ID is a lot more constant so the dart seal should be a bit better.



Q/C/F?