WARNING!!! This post s by a woodworker who knows nothing about lathe work. But.........
When looking for a bowel Gouge I got the same advice 3/8 & 1/2" But got confused because I found brands can be measured different. Some are measured by the flute width others by the width of the whole tip. So one brands 3/8 may be another brands 1/2"
Maybe some experienced turners on here could give a better explanation.
"Remember back in the day, when things were made by hand, and people took pride in their work?"
- Rick Dale