The term hardness is used in two senses, namely: (1) resistance to indentation, and (2) resistance to abrasion or scratching. In the latter sense hardness combined with toughness is a measure of the wearing ability of wood and is an important consideration in the use of wood for floors, paving blocks, bearings, and rollers. While resistance to indentation is dependent mostly upon the density of the wood, the wearing qualities may be governed by other factors such as toughness, and the size, cohesion, and arrangement of the fibres. In use for floors, some woods tend to compact and wear smooth, while others become splintery and rough. This feature is affected to some extent by the manner in which the wood is sawed; thus edge-grain pine flooring is much better than flat-sawn for uniformity of wear.

TABLE XII
HARDNESS OF 32 WOODS IN GREEN CONDITION, AS INDICATED BY THE LOAD REQUIRED TO IMBED A 0.444-INCH STEEL BALL TO ONE-HALF ITS DIAMETER
(Forest Service Cir. 213)
COMMON NAME OF SPECIES Average End surface Radial surface Tangential surface
PoundsPoundsPoundsPounds
Hardwoods



1 Osage orange 1,971 1,838 2,312 1,762
2 Honey locust 1,851 1,862 1,860 1,832
3 Swamp white oak 1,174 1,205 1,217 1,099
4 White oak 1,164 1,183 1,163 1,147
5 Post oak 1,099 1,139 1,068 1,081
6 Black oak 1,069 1,093 1,083 1,031
7 Red oak 1,043 1,107 1,020 1,002
8 White ash 1,046 1,121 1,000 1,017
9 Beech 942 1,012 897 918
10 Sugar maple 937 992 918 901
11 Rock elm 910 954 883 893
12 Hackberry 799 829 795 773
13 Slippery elm 788 919 757 687
14 Yellow birch 778 827 768 739
15 Tupelo 738 814 666 733
16 Red maple 671 766 621 626
17 Sycamore 608 664 560 599
18 Black ash 551 565 542 546
19 White elm 496 536 456 497
20 Basswood 239 273 226 217
Conifers



1 Longleaf pine 532 574 502 521
2 Douglas fir 410 415 399 416
3 Bald cypress 390 460 355 354
4 Hemlock 384 463 354 334
5 Tamarack 384 401 380 370
6 Red pine 347 355 345 340
7 White fir 346 381 322 334
8 Western yellow pine 328 334 307 342
9 Lodgepole pine 318 316 318 319
10 White pine 299 304 294 299
11 Engelmann pine 266 272 253 274
12 Alpine fir 241 284 203 235
NOTE. - Black locust and hickory are not included in this table, but their position would be near the head of the list.

Tests for either form of hardness are of comparative value only. Tests for indentation are commonly made by penetrations of the material with a steel punch or ball.16 Tests for abrasion are made by wearing down wood with sandpaper or by means of a sand blast.

[Footnote 16: See articles by Gabriel Janka listed in bibliography, pages 151-152.]