What are two bridge types located on a spectacle frame?

The correct answer is keyhole and saddle, as these are specific types of bridge designs that you can find on spectacle frames, which are the front part of eyeglasses that holds the lenses in place.

The keyhole bridge has a unique shape that resembles a keyhole, providing a secure fit on the nose while allowing for comfort and stability. This design is particularly useful for individuals with certain nose shapes or sizes, as it helps keep the spectacles in place without slipping.

The saddle bridge, on the other hand, has a more traditional design that creates a smooth curve across the nose. This bridge type distributes the weight of the glasses evenly and provides a comfortable resting point, which is essential for long-term wear.

In contrast, the other options do not correspond to commonly recognized classifications of bridge types on eyewear. For example, while arched and flat may describe general shapes, they do not denote specific bridge designs within the context of spectacle frames. Similarly, double and single or square and round do not accurately represent the terminology used to describe the technical features of eyeglass bridges. The focus on keyhole and saddle bridges emphasizes their relevance to functional and aesthetic choices in eyewear design.