Hello, and thanks for your question. It sounds like you actually need a solid flange neck to work with set screws in the fitter. Here's a link:
https://www.lamppostglobes.com/12-Inch-Frosted-Acrylic-Lamp-Post-Globe-with-391-Inch-Solid-Flange_p_619.html
If you need a fitter and socket to attach the globe to the post, here is the proper fitter:
https://www.lamppostglobes.com/4-Inch-Cast-Aluminum-Post-Top-Fitter_p_452.html
If you would like to stay with the 4 inch twist lock neck, we have those fitters as well:
https://www.lamppostglobes.com/Post-Top-Fitter-for-4-Inch-Twist-Lock-Lamp-Post-Globes_p_56.html
Thanks again for your question.
Justin