*(Ranked by Janka hardness rating)
The Janka (or side) hardness test measures the force
required to embed a .444-inch steel ball to half its diameter in wood.
It is one of the best measures of the ability of a wood species to withstand
denting and wear. By the same token, it is also a good indicator of
how hard or easy a species is to saw or mill.
*Source: "National Wood Flooring Association
Technical Publication No. A200", p.7: orig. from "Wood Handbook:
Wood as an Engineering Material", Agriculture Handbook 72, Forest
Products Laboratory, Forest Service, US Dept of Agriculture, revised