The charts to the right give the approximate pressure
required to make a 90 degree air bend in mild steel.
Bending pressures required for other metals compared
to 60,000 P.S.I. tensile mild steel on chart:

Soft aluminum - 50% of pressure listed
Aluminum Alloy (heat treated) - Same as listed
Stainless Steel - 50% more of pressure listed
 METRIC TONNAGE CHART
V(mm) 4 6 8 10 12 16 20 24 30 40 50 60 80 100 120 160
V(inch) 0.157" 0.236" 0.315" 0.394" 0.472" 0.630" 0.787" 0.945" 1.181" 1.575" 1.969" 2.362" 3.150" 3.937" 4.724" 6.299"
B(outside flange mm) 2.8 4.2 5.6 7.0 8.6 11.5 14.4 17 21 29 36 42.4 56.5 71 85 114
ri (mm) 0.6 1 1.2 1.5 1.8 2.4 3 3.6 4.5 6 7.5 9 12 15 18 24
 Thickness(mm)                                
0.5mm 4 2                            
1mm 10 8 5.5 4.5                      
1.2mm   16 12 9 7                      
1.5mm     20 14 11 8 6                  
2mm         22 15 11 9.5                
2.5mm           25 19 15 11              
3mm             28 22 17 12            
4mm               44 33 22.5 17          
5mm 55 37 29 22
6mm                   58 42 34        
8mm 83 65 45 35

10mm                       110 75 57 45  
12mm                         116 85 68  
14mm                           121 91 68
15mm                           143 112 79
16mm                           168 131 90
18mm                             172 119
20mm                             222 150
25mm                               254
INCH TONNAGE CHART
V(inch) 0.250" 0.375" 0.500" 0.625" 0.750" 0.875" 1.000" 1.125" 1.250" 1.500" 2.000" 3.000 4.000" 5.000" 6.000" 8.000"
V(mm) 6.4mm 9.5mm 12.7mm 15.9mm 19.05mm 22.2mm 25.4mm 28.6mm 31.8mm 38.1mm 50.8mm 76.2mm 101.6mm 127mm 152.4mm 203.2mm
B(outside flange inch) 0.167" 0.265" 0.354" 0.442" 0.530" 0.619" 0.707" 0.795" 0.866" 1.060" 1.414" 2.121" 2.828" 3.535" 4.242" 5.656"
ri (inch) 0.041" 0.063" 0.083" 0.104" 0.125" 0.146" 0.167" 0.188" 0.208" 0.250" 0.333" 0.500" 0.667" 0.833" 1.000" 1.333"
 Thickness (inch)                                
20 (0.036") 3.2 2.0
18 (0.048") 5.1 3.4 2.7 2.4                        
  16 (0.060")   5.8 4.0 3.1 2.5                    
14 (0.075")     6.9 5.0 4.0 3.5                    
12 (0.105") 8.3 6.9 5.6
11 (0.120")           9.9 8.2 7.2 5.4              
10 (0.135")           11.9 9.9 7.3 7.1 5.8            
3/16" (0.188")               14.3 14.2 12.2 7.5          
1/4" (0.250")                   23.7 16.5 11.4        
5/16" (0.313")                     27.0 19.7        
3/8" (0.375")                     42.3 30.9 22.8 16.9    
7/16" (0.438")                         32.2 24.3 19.4  
1/2" (0.500")                           34.6 27.0 18.3
5/8" (0.625")                             47.1 32.0
3/4" (0.750")                               50.4
7/8" (0.875")                               73.9
1"                               103.0