Narrow Rail Belt
The Narrow Rail belt is a 30mm (about 1.2") wide version of the standard Rail belt, with the same classic square buckle profile.
I don't believe in fashion rules, but narrower belts are generally considered more formal. This width is versatile, and also offers some variety if you have mostly wider belts in the closet.
Belts are made-to-order and cannot be returned or exchanged, so it's vital that you get your sizing right!