Perforation Uses | Ties
Per Inch | Perforation Types
Perforations are classified by bursting strength
and type. The bursting strength is referred to as "Ties
Per Inch" or TPI. The type of perforation
refers to it being horizontal or vertical on the unit set form. Horizontal
and vertical perforations can run across the full width and/or length
of the form or they can run a partial distance across the width and/or
length. Most unit sets have a full horizontal stub perf on each part.
The forms are glued together in the stub area to form a set. After
the form has been filled out, the stub is detached at the perforation
causing the parts to become detached from each other.
Ties Per Inch (TPI)
The tie or tab is the part of the perforation
where the paper does not get cut, but remains intact to "tie" the
paper together. The ties alternate with cut areas to form the perforation. The
tied areas of the perforation are usually narrower than the cut areas to allow
for easier detachment of the sections separated by the perforation. The proper
TPI to use is generally determined by the type of form and the function of the
perforation on that form. The following are some of the common TPI and their
uses on unit sets:
- 4 TPI: 4 TPI is most often used on the stub perforation of a unit
set form. It allows for easy removal of the stub for detachment of the individual
parts of the unit set.
- 6 TPI: 6 TPI is also used as a stub perf, but it does not detached
as easily as a 4 TPI. It is sometimes used for the stub perf on the first
and last parts of a unit set. It provides more strength to the entire set
so that the stubs will not loosen up before the end user is ready to detach
- 8 and 10 TPI: The 8 and 10 TPI perforations are most often used as
internal perfs on one or more of the parts of a unit set. They are used as
a perf within the form that allows the user to remove a section of the form.
- 12 TPI: 12 TPI is also referred to as a "statement perf".
It is most often used as a perf within the form that allows the user to remove
a section of the form. For example, the top or bottom section of a "statement
of account" form may be removed to be sent back with a payment. The 12
TPI perforation is durable and many times it is best to fold over the perf
so that it detaches easier.
- Letteredge or Invisible Perf: As the name implies, a letteredge perf
is nearly invisible and leaves a clean, smooth edge after the perf is detached.
It is most often used when a clean edge is required after detaching the stub,
such as on a letterhead. The most common ties per inch for letterhead perfs
are 50, 66, and 72. Most forms manufacturers use one of them as the standard
for all of their letteredge perfs unless a specific TPI is requested. A letteredge
perf does not work well on heavier weight stock. It is too difficult to control
the depth of the perforation which may result in a perforation that does not
detach properly. If you are unsure of which TPI to use, you should discuss
the options with your supplier.
- Horizontal perforations run parallel to the stub perf.
- The number and position of perforations is usually not critical
for full horizontal perforations.
- Partial horizontal perforations do not run the full width of the
- The number and position of partial horizontal perforations is
limited so consult your supplier for information on these limitations.
- Vertical perforations run down the length of the form, perpendicular
to the stub perforation.
- There are limitations on the number and positions of the perforations.
Consult you supplier for information on these limitations.
- Partial vertical perforations do not run the entire length of
the form and will have the same limitations as full vertical perforations.
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