Belt loops are a must on jeans.
More than 100 years have passed since it was first added in 1922.
Belt loops up to around 1950 have raised central portions.
The reason for this is to prevent thread fraying, which is popular with vintage enthusiasts.
However, belt loops since the 1950s have not changed much.
By the way, there are also belt loops with red selvedge hidden inside.
If you find this, you are lucky, so get it now.