Corrugated Flutes

Official definitions of the different corrugated flute types can vary, the ones below are from BS 1133 section 7.5.

Details of Flute Forms - Metric
Flute Form Approx. Corrugations per Meter Approx. Height of Corrugations Typical Draw Factors
A Flute 105 to 125 4.5 to 4.7 mm 1.55 +/- 5%
B Flute 150 to 185 2.1 to 2.9 mm 1.33 +/- 5%
C Flute 120 to 145 3.5 to 3.7 mm 1.44 +/- 5%
E Flute 290 to 320 1.1 to 1.2 mm 1.27 +/- 5%

The caliper of the liners and fluting medium used for a particular board, would be added to the flute height to give the overall board caliper. Below are the measurements in Imperial units.

Details of Flute Forms - Imperial
Flute Form Approx. Corrugations per Yard Approx. Height of Corrugations Typical Draw Factors
A Flute 96 to 114 0.1772 to 0.185" 1.55 +/- 5%
B Flute 137 to 169 0.0827 to 0.1142" 1.33 +/- 5%
C Flute 110 to 133 0.1378 to 0.1457" 1.44 +/- 5%
E Flute 265 to 293 0.0433 to 0.0472" 1.27 +/- 5%

The measurements used in design allowance calculations are usually standardized and rounded. The table below shows the general values usually used for design allowances.

Flute Millimeters Inches Inches
A 6 0.25 1/4
B 3 0.125 1/8
C 5 0.1875 3/16
E 2 0.0625 1/16
F 1 0.04688 3/64
G 0.7 0.03125 1/32
N 0.5 0.01563 1/64
EB 5 0.1875 3/16
BC 8 0.3125 5/16
CA 11 0.4375 7/16
AB 9 0.375 3/8
AAC 14 0.5625 9/16
AAA 16 0.625 5/8