Tolerance

MOLDED RUBBER TOLERANCE:

Rubber tolerances are described in Rubber Manufacturers Association (RMA) Handbook.
A1 Tolerance (High Precision)
A2 Tolerance (Precision)
A3 Tolerance (Commercial)
A4 Tolerance (Basic)

This publication is called the RMA Handbook because the ARPM (Association for Rubber Products Manufacturers) was originally known as the Rubber Manufacturers Association (RMA)

The A2 ‘precision’ tolerances provide higher precision over A3 general purpose tolerance. The A1 ‘high precision’ tolerances can be achieved by individually inspecting and selecting ‘high precision’ tolerances meeting o-rings. A higher precision comes with a higher cost so overall cost benefit analysis should be done to choose the right tolerances. Most O-Rings are high quality ‘precision’ parts which conforms to A2 ‘precision’ tolerance of the RMA Handbook. Most other rubber products use A3 ‘general purpose’ tolerances with good results. The rubber can stretch and bend without sacrificing performance so much more forgiving tolerances are used. Extruded rubber (cords) has its own tolerances. Rigid metal tolerances and application methods should not be used in measuring O-Rings. An O-Ring will have two tolerances; ‘Fixed’ and ‘Closure’. Fixed tolerances specify side tolerances. Closure tolerances specify up and down tolerance in respect to the mold orientation. The drawing illustrates these tolerances.

Molded Products

A1 High Precision      
 Size (mm) Tolerance    Size (inch) Tolerance  
 Above  Incl Fixed closure  Above  Incl Fixed closure
      –       10 ±0.10 ±0.13       –    0.400 ±0.004 ±0.005
     10      16 ±0.13 ±0.16   0.400   0.630 ±0.005 ±0.006
     16      25 ±0.16 ±0.20   0.630   1.000 ±0.006 ±0.008
     25      40 ±0.20 ±0.25   1.000   1.600 ±0.008 ±0.010
     40      63 ±0.25 ±0.32   1.600   2.500 ±0.010 ±0.013
     63     100 ±0.32 ±0.40   2.500   4.000 ±0.013 ±0.016
    100  >160 ±0.40 ±0.50   4.000   6.300 ±0.016 ±0.020
               
A2  Precision      
 Size (mm) Tolerance    Size (inch) Tolerance  
 Above  Incl Fixed closure  Above  Incl Fixed closure
      –       10 ±0.16 ±0.20       –    0.100 ±0.006 ±0.008
     10      16 ±0.20 ±0.25   0.100   0.630 ±0.008 ±0.010
     16      25 ±0.25 ±0.32   0.630   1.000 ±0.010 ±0.013
     25      40 ±0.32 ±0.40   1.000   1.600 ±0.013 ±0.016
     40      63 ±0.40 ±0.50   1.600   2.500 ±0.016 ±0.020
     63     100 ±0.50 ±0.63   2.500   4.000 ±0.020 ±0.025
    100     160 ±0.63 ±0.80   4.000   6.300 ±0.025 ±0.032
    160  >160 trim size×0.004 trim size×0.005   6.300  >6.300 trim size×0.004 trim size×0.005
               
A3  Commercial      
 Size (mm) Tolerance    Size (inch) Tolerance  
 Above  Incl Fixed closure  Above  Incl Fixed closure
      –       10 ±0.20 ±0.32       –    0.400 ±0.008 ±0.013
     10      16 ±0.25 ±0.40   0.400   0.630 ±0.010 ±0.016
     16      25 ±0.32 ±0.50   0.630   1.000 ±0.013 ±0.020
     25      40 ±0.40 ±0.63   1.000   1.600 ±0.016 ±0.025
     40      63 ±0.50 ±0.80   1.600   2.500 ±0.020 ±0.032
     63     100 ±0.63 ±1.00   2.500   4.000 ±0.025 ±0.040
    100     160 ±0.80 ±1.25   4.000   6.300 ±0.032 ±0.050
    160  >160 trim size×0.005 trim size×0.008   6.300  >6.300 trim size×0.005 trim size×0.008
               
A4 Basic      
 Size (mm) Tolerance    Size (inch) Tolerance  
 Above  Incl Fixed closure  Above  Incl Fixed closure
      –       10 ±0.32 ±0.82       –    0.400 ±0.013 ±0.032
     10      16 ±0.40 ±0.90   0.400   0.630 ±0.016 ±0.036
     16      25 ±0.50 ±1.00   0.630   1.000 ±0.020 ±0.040
     25      40 ±0.63 ±1.12   1.000   1.600 ±0.025 ±0.045
     40      63 ±0.80 ±1.25   1.600   2.500 ±0.032 ±0.050
     63     100 ±1.00 ±1.40   2.500   4.000 ±0.040 ±0.056
    100     160 ±1.25 ±1.60   4.000   6.300 ±0.050 ±0.063
    160  >160 trim size×0.008 trim size×0.010   6.300  >6.300 trim size×0.008 trim size×0.010

Extruded Rubber Products (cords)

E1 High Precision
E2 Precision
E3 Commercial

APRM Class High Precision Precision Commercial
Drawing Designation E1 E2 E3
Dimensions (millimeters)
Over Through      
0.0 1.5 ±0.15 ±0.25 ±0.40
1.5 2.5 0.20 0.35 0.50
2.5 4.0 0.25 0.40 0.70
4.0 6.3 0.35 0.50 0.80
6.3 10.0 0.40 0.70 1.00
10.0 16.0 0.50 0.80 1.30
16.0 25.0 0.70 1.00 1.60
25.0 40.0 0.80 1.30 2.00
40.0 63.0 1.00 1.60 2.50
63.0 100.0 1.30 2.00 3.20

APRM Class High Precision Precision Commercial
Drawing Designation E1 E2 E3
Dimensions (inches)
Over Through      
0.000 0.060 ±0.006 ±0.010 ±0.015
0.600 0.100 0.008 0.014 0.020
0.100 0.160 0.010 0.016 0.027
0.160 0.250 0.014 0.020 0.031
0.250 0.390 0.016 0.027 0.039
0.390 0.630 0.020 0.031 0.051
0.630 0.980 0.027 0.039 0.063
0.980 1.570 0.031 0.051 0.079
1.570 2.480 0.039 0.063 0.098
2.480 3.940 0.051 0.079 0.126