Frame Measurements and Markings
Fmiliarity with frame measurements and how theyare marked is essential to proper ordering of pre-
scriprion glasses. Knowledge of measurement procedures assures receipt Of the proper size when ordering a replacement for a broken part. The purpose of this chapter is to give the reader a complete understanding of frame dimensional properties. The confidence and capability achieved as a result of this is the base on which to develop skill in frame selection.
THE OLDER DATUM SYSTEM
The previously used datum system for measuring lenses was established as a system of reference points for frames and lenses so thar placemenr of lens optical centers and
bifocal segment heights would be consistent.
With the lens placed as it should sit in the frame, horizontal lines were drawn at the highest and lowest edges of the lens (Figure 2-1). A line drawn halfway between the two horizontal lines and parallel to them was known as the dunnn line. The width of the lens along this line was called the datum length or eye size. The point along the datum line halfway between the edges Of the lens is the renter. The depth Of the lens, is the datum center. The depth Of the lens, measured as the vertical depth through the datum center, was the mid-datum depth. he datum system preceded the currently used boxing system.
THE BOXING SYSTEM
The boxing system improved on the foundation provided by the datum system. The datum system used two horizontal lines—one against the top and the other against the bottom of the lens. The boxing system kept these two horizontal lines and added two vertical lines.
These vertical lines are placed against right and left edges Of the lens. All four lines form a box around the lens
Horizontal Midline There is a horizontal line halfway between the top and
bottom of rhe lens. In the datum system, this was called the datum line. This name continues to be used. However, in the boxing system, this line is more commonly referred to as the horizontal midline or the ISO- degree line.
Geometric Center
The center of the lens is the point on the horizontal midline halfway between the two lens-bordering vertical lines. It is known as the geometric center or hoeing center of the edged lens. This term does not imply anything about the optical positioning of the lens.
Size
The size of the lens then is the length and depth of the box containing the lens. The horizontal length is now commonly referred to as the eye size when referring to the frame and the lens size when referring to the lenses.
Both are measured in millimeters.
most practitioners speak of lens size or eye size, they are referring primarily to the horizontal measure
of the lens, denoted by the letter "A" in Figure 2-2. Some frames list an eye size value that is different from and unrelated to the frame A dimension. Such procedures attempt to relate this eye size number to a "fitting value." ThiS IS not a recommended practice and leads to confusion.
This is not a recommended practice and leads to confu-
Sion, but is so commonplace that frame reference materials will usually list both an A dimension and an eye size, even if they are the same value.
The letter "B" denotes the vertical measure of the box enclosing the lens. Both "A" and "B" are in a sense independent of lens shape. The letter "C" refers to the width of the lens itself along the horizontal midline.l (This can vary considerably from the A dimension.) The C dimension Of a lens is seldom used. In the Older datum system, this was the eye size of the frame. Some people still
mistakenly measure the eye size this way.
The C dimension of a lens should not be confused with the "C-size" of a lens. C-size is the circumference of the edged lens and is sometimes used to increase accuracy when duplicating an Old lens size When edging. Measurement
In determining the horizontal boxing dimensions of a frame, the measurement begins at the inside of the groove
on the left side Of the imaginary enclosing box and extends horizontally across the lens opening to the farthest part of the groove on the right side of the box
(Figure 2-3). Do not rilr the box.
In measuring a lens, the measurement begins at the
apex, or point, of the bevel on the left side of the box
enclosing the lens and extends to the apex of the bevel
on the right side of the box. Remember, the A dimension
is the width of the enclosing box. It is not the width of
the lens at the middle of the shape.
Effective Diameter
The effective diameter ofa lens is found by doubling the
distance from the geometric center of the lens to the
apex of rhe lens bevel farthest from ir (see Figure 2-2).
Frame Difference
The difference between the horizontal and the vertical
measurements is known as the frame difference and is
measured in millimeters. The larger the difference, the
more rectangular the enclosing box appears (Figure 2-4).
Frame difference is sometimes referred to as lens
difference.
Distance Between Lenses (DBL) or Bridge Size
The boxing System also makes it possible to define the
distance between lenses (DBL). The DBL is the distance
between the two boxes when both lenses are boxed off
in the frame. This is usually synonymous with bridge
size, although it is important to note that manufacturers
not adhering to the boxing system may mark a bridge
size that does not correspond to the distance between
lenses.
Bridge size or is measured on the frame as the
distance from the inside nasal eyewire grooves across the
bridge area at the narrowest point (Figure 2-5). This
distance below or above the horizontal midline (called
seg 'imp or seg raise), or (2) the distance from the lower
line of the boxing system rectangle enclosing the lens
shape (called seg height). In the actual measuring process,
the level Of the lower line Of the box corresponds to the
lowest point in the eyewire groove. "Ibis he dif-
the depth of rhe pomr rm the lens edge found
directly below the pupil as can be seen by looking carefully
at Figure 2-2.
TEMPLE LENGTH
Most temples are currently marked with the total, or
overall, temple length. Temple lengths are expressed in
millimeters. Temple length may be measured in one of
the following ways.
Overall Temple Length
The overall temple length is the distance from the center
Of the center barrel Scnw hole to the posterior end Of
the temple, measured along the center of (he temple
(Figure 2-6, A). Many times the center of the barrel
• The term •Frame rnay have originated when frame Size wag
detemlined hy selecting the correctly fitting hridEe size, then
ing an size so that wearer's pupils be at the geometric
, DBL, and temple length. Metal
measurements: eye Size
frames that are manufactured from "rolled gold" are also
marked as to the amount of gold found in the frame.
Rolled gold frames were used regularly a good While ago.
Any new rolled gold frames are very expensive.
Eye Size and DBL
When a frame marking such as is seen, it means
that the cyc size is 50 mm and the distance between
lenses is 20 mm. The box bet-ween the numbers means
that the eye size is measured according to the boxing
method; it also serves to separate the two numbers and
prevent confusion. The eye size and DBL are sometimes
simply marked 50-20 or 50/20.
Location Of Markings
On a plastic _frame the marking may be found in any Of several places. It may be printed on the inside of the nose pad, or it may be found on the upper outer section
Of the eyewire. Some frames had the size printed On the back side of the endpiece, and the temple must be folded closed to find it. Sometimes the eye size is printed on
one end piece and the DBL on the other. As it should be, temple length is printed on the inner side of the temples.
Some manufacturers put all three measurement of the temple. This is done because most frames are sold as a complete unit.
set Of temples. Unfortunately this leads to confusion
when temples are exchanged.
On met"/ frames and frames with metal chassis, the
eye size and DBL are usually on the inside of the bridge,
although occasionally they are printed on the underside
of a top reinforcing bar, or again, on the temples.
Frame Manufacturer Name, Color, and Country
of Origin
Frames should also be marked as to country of origin,
manufacturer, and frame name. Many frame manufac-
turers use a number rather than a name. This can be
confusing if the frame color is also specified by number
and both numbers are stamped on the frame. Consulting
a frame reference catalog or database will help.
Safety Frame Markings
Frames that are suitable for use as safety glasses must
have "7.87" or "7.87-2" and the name or logo of the
manufacturer stamped on the frame front and on both
temples. This is as specified by the American National
Standards Institute (ANSI) in their standard called
American Nation"/ Practice for Occupational
Edut-otirm,'/l Eye Fac•e Protection . The standard is num-
bered as 7-87.1. If a pair Of glasses has safety lenses, but
is not in a frame marked "7-87" or "7.87-2," the lasses
Copyfish
Of metal is used in combination with gold to make the
gold alloy.
The learat system is used to determine the amount of
gold present. The number marked on the article is the
amount Of gold by weight in comparison to a total of 24
units: an article marked 12k is an alloy made up of one-
half gold and one-half another metal.
Fine Gold
Fine gold is the name used for an article that has no metal
in it other than gold. The gold found in it is chemically
pure. Although this is the purest form, it is not always
the most practical, as is the case in spectacle frames.
Frames Of fine gold would be too lnalle•able and would
bend and dent too easily to be practical. Using the karat
system, fine gold is 24 karats fine, which means that by
weight, 24 parts Out Of 24 are gold.
Solid Gold
Solid gold articles are actually an alloy of gold and another
metal, a mixture Of gold and a base metal. Thus the term
is misleading, as it does not mean all gold. The solid gold
article is made entirely of the gold alloy. It maintains its
luster regardless of how far down it is worn through
"Vhe svmbol 8is used to denotea 10k solid old bridge;
Fmiliarity with frame measurements and how theyare marked is essential to proper ordering of pre-
scriprion glasses. Knowledge of measurement procedures assures receipt Of the proper size when ordering a replacement for a broken part. The purpose of this chapter is to give the reader a complete understanding of frame dimensional properties. The confidence and capability achieved as a result of this is the base on which to develop skill in frame selection.
THE OLDER DATUM SYSTEM
The previously used datum system for measuring lenses was established as a system of reference points for frames and lenses so thar placemenr of lens optical centers and
bifocal segment heights would be consistent.
With the lens placed as it should sit in the frame, horizontal lines were drawn at the highest and lowest edges of the lens (Figure 2-1). A line drawn halfway between the two horizontal lines and parallel to them was known as the dunnn line. The width of the lens along this line was called the datum length or eye size. The point along the datum line halfway between the edges Of the lens is the renter. The depth Of the lens, is the datum center. The depth Of the lens, measured as the vertical depth through the datum center, was the mid-datum depth. he datum system preceded the currently used boxing system.
THE BOXING SYSTEM
The boxing system improved on the foundation provided by the datum system. The datum system used two horizontal lines—one against the top and the other against the bottom of the lens. The boxing system kept these two horizontal lines and added two vertical lines.
These vertical lines are placed against right and left edges Of the lens. All four lines form a box around the lens
Horizontal Midline There is a horizontal line halfway between the top and
bottom of rhe lens. In the datum system, this was called the datum line. This name continues to be used. However, in the boxing system, this line is more commonly referred to as the horizontal midline or the ISO- degree line.
Geometric Center
The center of the lens is the point on the horizontal midline halfway between the two lens-bordering vertical lines. It is known as the geometric center or hoeing center of the edged lens. This term does not imply anything about the optical positioning of the lens.
Size
The size of the lens then is the length and depth of the box containing the lens. The horizontal length is now commonly referred to as the eye size when referring to the frame and the lens size when referring to the lenses.
Both are measured in millimeters.
most practitioners speak of lens size or eye size, they are referring primarily to the horizontal measure
of the lens, denoted by the letter "A" in Figure 2-2. Some frames list an eye size value that is different from and unrelated to the frame A dimension. Such procedures attempt to relate this eye size number to a "fitting value." ThiS IS not a recommended practice and leads to confusion.
This is not a recommended practice and leads to confu-
Sion, but is so commonplace that frame reference materials will usually list both an A dimension and an eye size, even if they are the same value.
The letter "B" denotes the vertical measure of the box enclosing the lens. Both "A" and "B" are in a sense independent of lens shape. The letter "C" refers to the width of the lens itself along the horizontal midline.l (This can vary considerably from the A dimension.) The C dimension Of a lens is seldom used. In the Older datum system, this was the eye size of the frame. Some people still
mistakenly measure the eye size this way.
The C dimension of a lens should not be confused with the "C-size" of a lens. C-size is the circumference of the edged lens and is sometimes used to increase accuracy when duplicating an Old lens size When edging. Measurement
In determining the horizontal boxing dimensions of a frame, the measurement begins at the inside of the groove
on the left side Of the imaginary enclosing box and extends horizontally across the lens opening to the farthest part of the groove on the right side of the box
(Figure 2-3). Do not rilr the box.
In measuring a lens, the measurement begins at the
apex, or point, of the bevel on the left side of the box
enclosing the lens and extends to the apex of the bevel
on the right side of the box. Remember, the A dimension
is the width of the enclosing box. It is not the width of
the lens at the middle of the shape.
Effective Diameter
The effective diameter ofa lens is found by doubling the
distance from the geometric center of the lens to the
apex of rhe lens bevel farthest from ir (see Figure 2-2).
Frame Difference
The difference between the horizontal and the vertical
measurements is known as the frame difference and is
measured in millimeters. The larger the difference, the
more rectangular the enclosing box appears (Figure 2-4).
Frame difference is sometimes referred to as lens
difference.
Distance Between Lenses (DBL) or Bridge Size
The boxing System also makes it possible to define the
distance between lenses (DBL). The DBL is the distance
between the two boxes when both lenses are boxed off
in the frame. This is usually synonymous with bridge
size, although it is important to note that manufacturers
not adhering to the boxing system may mark a bridge
size that does not correspond to the distance between
lenses.
Bridge size or is measured on the frame as the
distance from the inside nasal eyewire grooves across the
bridge area at the narrowest point (Figure 2-5). This
seg 'imp or seg raise), or (2) the distance from the lower
line of the boxing system rectangle enclosing the lens
shape (called seg height). In the actual measuring process,
the level Of the lower line Of the box corresponds to the
lowest point in the eyewire groove. "Ibis he dif-
the depth of rhe pomr rm the lens edge found
directly below the pupil as can be seen by looking carefully
at Figure 2-2.
TEMPLE LENGTH
Most temples are currently marked with the total, or
overall, temple length. Temple lengths are expressed in
millimeters. Temple length may be measured in one of
the following ways.
Overall Temple Length
The overall temple length is the distance from the center
Of the center barrel Scnw hole to the posterior end Of
the temple, measured along the center of (he temple
(Figure 2-6, A). Many times the center of the barrel
• The term •Frame rnay have originated when frame Size wag
detemlined hy selecting the correctly fitting hridEe size, then
ing an size so that wearer's pupils be at the geometric
, DBL, and temple length. Metal
measurements: eye Size
frames that are manufactured from "rolled gold" are also
marked as to the amount of gold found in the frame.
Rolled gold frames were used regularly a good While ago.
Any new rolled gold frames are very expensive.
Eye Size and DBL
When a frame marking such as is seen, it means
that the cyc size is 50 mm and the distance between
lenses is 20 mm. The box bet-ween the numbers means
that the eye size is measured according to the boxing
method; it also serves to separate the two numbers and
prevent confusion. The eye size and DBL are sometimes
simply marked 50-20 or 50/20.
Location Of Markings
On a plastic _frame the marking may be found in any Of several places. It may be printed on the inside of the nose pad, or it may be found on the upper outer section
Of the eyewire. Some frames had the size printed On the back side of the endpiece, and the temple must be folded closed to find it. Sometimes the eye size is printed on
one end piece and the DBL on the other. As it should be, temple length is printed on the inner side of the temples.
Some manufacturers put all three measurement of the temple. This is done because most frames are sold as a complete unit.
when temples are exchanged.
On met"/ frames and frames with metal chassis, the
eye size and DBL are usually on the inside of the bridge,
although occasionally they are printed on the underside
of a top reinforcing bar, or again, on the temples.
Frame Manufacturer Name, Color, and Country
of Origin
Frames should also be marked as to country of origin,
manufacturer, and frame name. Many frame manufac-
turers use a number rather than a name. This can be
confusing if the frame color is also specified by number
and both numbers are stamped on the frame. Consulting
a frame reference catalog or database will help.
Safety Frame Markings
Frames that are suitable for use as safety glasses must
have "7.87" or "7.87-2" and the name or logo of the
manufacturer stamped on the frame front and on both
temples. This is as specified by the American National
Standards Institute (ANSI) in their standard called
American Nation"/ Practice for Occupational
Edut-otirm,'/l Eye Fac•e Protection . The standard is num-
bered as 7-87.1. If a pair Of glasses has safety lenses, but
is not in a frame marked "7-87" or "7.87-2," the lasses
Copyfish
Of metal is used in combination with gold to make the
gold alloy.
The learat system is used to determine the amount of
gold present. The number marked on the article is the
amount Of gold by weight in comparison to a total of 24
units: an article marked 12k is an alloy made up of one-
half gold and one-half another metal.
Fine Gold
Fine gold is the name used for an article that has no metal
in it other than gold. The gold found in it is chemically
pure. Although this is the purest form, it is not always
the most practical, as is the case in spectacle frames.
Frames Of fine gold would be too lnalle•able and would
bend and dent too easily to be practical. Using the karat
system, fine gold is 24 karats fine, which means that by
weight, 24 parts Out Of 24 are gold.
Solid Gold
Solid gold articles are actually an alloy of gold and another
metal, a mixture Of gold and a base metal. Thus the term
is misleading, as it does not mean all gold. The solid gold
article is made entirely of the gold alloy. It maintains its
luster regardless of how far down it is worn through
"Vhe svmbol 8is used to denotea 10k solid old bridge;
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