I made my own Barlow DIY lens using plumbers tubing for a sink. The tubing is hard plastic and easily fastens to the eyepiece using the twist connector.
The tubing is seven inches from the bottom of the eyepiece to the top of the lens that can be screwed into the bottom of the tube opposite the eyepiece.
What type of magnification am I getting with the seven inch DIY Barlow Lens?
Here is a photo of the DIY Barlow Lens.
https://i.ibb.co/s1Z9Cqh/20190824-203804.jpg
This photo is the DIY Barlow being used as an extension without the lens.
https://i.ibb.co/WVK07Lg/20190824-180334.jpg