The ASTM D2240 standard covers type A, B, C, D, DO, and OO durometers. The most popular durometers are the types A and D. Very soft materials are rated on the Shore OO scale. Rubber and polyurethane are rated on the Shore A scale and hard materials are rated on the Shore D scale.
Type A - Soft Rubber, Elastomers, Waxes, Printing Rollers.
Type OO - Sponge Rubber, Very soft Rubber
The following is the conversion:
A OO
100
95
90
85
80 98
75 97
70 95
65 94
60 93
55 91
50 90
45 88
40 86
35 83
30 80
25 76
20 70
15 62
10 55
5 45