Hardness

VS (very soft) 480 kg/m3 or less
S (soft) 485 - 560 kg/m3
F (firm) 565 - 680 kg/m3
M (moderate) 685 - 800 kg/m3
H (hard) 805 - 960 kg/m3
VH (very hard) 965 kg/m3 or more

Strength Groups

S Unseasoned - There are seven groups ranging downward from S1 to S7.
SD Seasoned - There are eight groups ranging downward from SD1 to SD8.

Joint Groups

There are six groups ranging downward from 1 to 6; they indicate mechanical properties for jointing purposes in engineering design.