What are the parts of a belt called?
The strap is the flexible, non-mechanical part of the belt, that goes around the wearer's waist. Can be made of leather, a textile, or a synthetic.
Within this is the loop, which is meant to keep the end of the strap in place, on the part that overlaps, once it's gone all the way around the wearer's waist.
The buckle collectively refers to the metal hardware that is affixed to one end of the belt. It can either be one piece, or can consist of multiple pieces such as in the image below.
The outer portion is called the frame. The bar that goes across is called the prong. When the other end of the belt goes around, it goes through the frame, as shown below.

Once the belt is at the desired tightness, the prong will go through one of the holes on the strap, and hold the belt in that position.

Some belts may also have what is known as an end tip. An end tip is usually made of metal, and protects the end of the strap that is opposite the buckle.

The end tip can be greatly beneficial, as when the belt comes on and off, the end of the strap that goes through the buckle can become frayed from friction with the buckle, loop, or parts of the wearer's clothing.

So, in sum, that's 
- Strap
- Loop
- Buckle (frame, prong)
- End tip

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