26 
BULLETIN 440, U. S. DEPARTMENT OF AGRICULTUKE. 
on the machines after they arrive in the woods. Three types of 
efficient spark arresters are in use, varying in price from S12 to $45. 
Because of the increase in size of yarding engines, there is a ten- 
dency to use heavier wire rope for yarding. At present the most 
satisfactory sizes for main lines are 1 inch for the small yarders, 
l|-inch for all ordinary yarders, and 1^-inch for the larger yarders 
in rough country with uphill hauls. The universal back line is 
five-eighths inch, except for very small machines, upon which one- 
half inch is sometimes used. Dolbeers are commonly equipped with 
seven-eighths-inch main line and three-eighths-ineh back line. 
Wire rope for logging is commonly quoted at list prices upon which 
certain discounts are allowed, varying from time to time with the 
price of steel. There are two grades, plow steel and extra plow steel. 
Most logging rope is the latter grade. Yarding rope is commonly 
composed of 6 strands of 19 wires, each about a hemp center. On 
account of its greater pliability, rope having 8 strands of 19 wires 
each is preferred for chokers. Table 4 gives approximate net prices 
in 191-4 per linear foot for standard logging wire rope f. o. b. San 
Francisco. 
Table 4. — Approximate net prices for standard logging wire rope in 1914 at San Francisco. 
Diam- 
eter. 
Weight 
per foot. 
Plow 
steel. 
6 bv 19. 
0.62 
.89 
1.20 
1.58 
2.00 
2.45 
3.00 
3.55 
SO. 06 
.085 
.115 
.15 
.19 
.24 
.29 
41 
Extra 
Extra 
plow 
plow 
steel. 
steel, 
6 by 19. 
Sby 19. 
Per foot. 
Per foot. 
§0.0S 
.11 
$0.12 
.15 
.17 
.19 
.245 
, 27 
.30 
.33 
.37 
.40 
.44 
.48 
.54 
.58 
Usually four or five chokers are kept on hand at each machine. 
Each consists of a piece of cable from 15 to 30 feet in length, having 
a loop on one and a choker hook on the other. They may be made 
of old yarding cable or new 1-inch 8 by 19 strand. 
The proper block equipment for a yaider consists of two ''Tommy 
Moores" or "Jumbos" for the yarding line, and one head or tail block 
and about six 10 or 12 inch trip-line blocks for the back line. 
Shackle yarding blocks are still used in a few instances but are 
rapidly being supplanted by the "Jumbos," since the latter permit 
the passage of the butt hook and chokers on the outward trip. A 
moving block is sometimes added to the equipment of a yarder, 
though usually one of the " Jumbos'' is used for moving. Table 5 
gives the approximate cost of the best grade of logging blocks f. o. b. 
San Francisco. 
