Perforations Printing Knowledge

Perforation Uses | Ties Per Inch | Perforation Types

Perforation Uses

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 the stub. 
  • 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.


Perforation Types

Horizontal Perforation:

  • 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 form.
  • The number and position of partial horizontal perforations is limited so consult your supplier for information on these limitations.


Vertical Perforation:

  • 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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