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Glossary/Tolerances Perforated Metal
 Perforations
Round Perforations – Staggered (60 degree pattern) is standard.
Variations include 45 Degree Staggered, and Straight Line Pattern
Square Perforations – Staggered Pattern or Straight Line Pattern
Slotted Perforations – Side Staggered, End Staggered, or Straight
Lines. Slotted Perforations will be round end slots; specify if
square end slots are required.
Pattern of Perforations
Unfinished End Pattern – The condition which occurs with some
specifications of staggered pattern perforations as a result of
tool design. On one end of the plate, the pattern will appear to
be incomplete due to unperforated holes in the even numbered rows
while on the other end of the same plate, the pattern will appear
to be imcomplete die to unperforated holes in the odd-numbered
rows.
Finished End Pattern – The condition which occurs with some
specifications of staggered pattern perforations as a result of
tool design, where the pattern is completed on both ends of the
plate.
Staggered Perforations, both round and square – Direction of the
stagger will normally be the short dimension of the sheet, as
illustrated in Fig. No.3 Straight row of holes is normally
parallel to long dimension of sheet.
Slotted Perforations – The long dimension of the slots can be
furnished parallel with either the width or length of the sheet in
most cases.
Formulas for Determining Percentage of Open Area
Staggered Round Holes
Square Holes (Straight or Staggered)
45 Degree Staggered Centers Pattern (Special)
Straight Round Holes
Square End Slot
Margins
Perforated Stock Size Sheets and Plates – The long sides of the
sheet will be supplied with minimum margins. The short sides of
the sheet will have either minimum margins or no margins
Sheets and Plates Resheared after Perforating – Special margins
are available to specifications but they must carry a tolerance
within the limits of the perforating tool. Unifinished end pattern
is standard in the industry.
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