Thick wall cylinder isn't exactly for Girth.
The point of a Thick Wall Cylinder is to add Weight, to PULL on your ligament and create a stretching effect at the same time that you pump.
Thick Wall Cylinders are also cut straight - Not flared for comfort, so they tend to "Dig" in when used. They dig in, and pull on the root Deep.
A regular or flared cylinder is more for comfort.
Thickwall and Regular cylinders can help with Girth, but it depends on what size you use.
Go to big - You'll pull in your scrotum and your balls.
Go to Small - You'll focus on length improvements.
Generally the recommended size charts will improve on both - length and girth.