Shore A scale is for testing the following
Rubber: Soft vulcanized (ie tyre), natural
(rubber & rubber like): GR-S, GR-1, neopene, thiokol, flexible polyacrylic
esters neoprene, thiokol, flexible polyacrilic
Other: Wax, felt, leather etc. (materials that
normally yield under fingernail pressure, such
as the heel on your shoe).
Shore D scale is for testing the following
Plastics: Harder grades such as rigid thermoplastics,
plexiglass, thermoploystrene, vinyl, sheet,
cellulode acetate, thermosetting
Other: Paper filled calendar rolls, calendar
bowls, etc. (materials that would not normally
indent under fingernail pressure, such as a pocket
comb or bowling ball).