The middle part of a pair of spectacles is called a bridge or a nose bridge. This is the part of the spectacle frame that forms a bridge from one side of your nose to the other.
It is called the ordinate.
Those numbers are called factors. A pair of those is called a factor pair.
There is no specific name - other than what you used: "a pair of parallel line segments".
The pair of numbers used to locate a point on a grid is called coordinate points.
They are called a linear pair.
a pair of spectacles
A pair of spectacles is a pair of lenses set in a frame worn on the nose and ears in order to correct deficiencies in eyesight.
Spectacles, goggles, Coke-bottle bottoms
A Pair of Spectacles - 1908 was released on: USA: 23 November 1908
Frame
i have two pair of specticales.
A pair of spectacles, or a monocle.
The noun spectacles is a shortened form for the term 'pair of spectacles'. The plural form is two pairs of spectacles.The nouns spectacles belongs to a group of nouns that are a shortened form for 'a pair of', for example:binocularsglassespantsscissorsshearsshortsspectaclestongstrouserstweezersAll of these nouns are made plural by changing 'a pair of...' to 'pairs of...'.
The curved glass in a pair of spectacles is called a lens. You will find that most spectacles are fitted with plastic lenses rather than glass lenses. The curvature of the lens determines the power/prescription/lens strength. Lens thickness, weight and curvature will vary from person to person depending on what type of prescription they need.
If a person is wearing spectacles it means he is wearing a pair of glasses. The word spectacles is rarely used in this day and age.
There is no specific collective noun for spectacles. Use the collective noun appropriate for the situation; for example a display of spectacles (in a shop), a collection of spectacles (in a drawer), a spectrum of spectacles (in an alliteration or a poem), etc.
Pince-nez is what this type of glasses is called. The name comes from French, meaning "Pinch nose".