32 BULLETIN 1436, U. S. DEPARTMENT OF AGRICULTURE 
from the dogwood trees available to-day. Unlike shuttle blocks, 
properly cared for bolts of this kind are large enough to resist the 
internal stresses which cause bursting. 
The shape of mallet heads varies. The two shown in Figure 19 
are well-balanced heads, the one barrel-shaped, and the other cylin- 
drical, both with beveled edges to prevent brooming. After being 
turned to the proper size the heads are sanded to a fine finish and the 
hole for the handle is bored. 
Boring is often the test of careful and uniform seasoning. If the 
seasoning has been so conducted that drying is only partially effected 
and a casehardened shell surrounds a still moist center, the head is 
likely to burst open, at times with a sharp report. This tendency 
is due to the release of internal stresses set up by improper season- 
ing, and results principally from drying bolts in a dryer in which the 
drying conditions can not be controlled, or by exposing them to the 
hot sun. 
Dogwood bolts, air- seasoned for mallet heads should be piled on 
sills off the ground so that air can circulate and in dry locations 
away from water or mud where weeds grow. They should also be 
protected by a roof from rain, snow, and sun, 
TURNPINS 
For shaping the ends of lead pipe, plumbers prefer dogwood turn- 
pins (fig. 19) as they satisfactorily withstand battering and rough 
usage. The turnpins are made in various sizes on a lathe from 
round stock, and are sanded and coated with shellac before being 
sold. 
MINE SPRAGS AND ROLLERS 
A mine sprag (fig. 19) is a cylindrical piece of wood, generally 
with the bark on, pointed at both ends, about 21 inches long and 
from 2V4 to 3V2 inches in diameter. It is used in coal-mining opera- 
tions as a braking device on mine cars that are not provided with 
brakes. By jamming a sprag between the spokes of a rotating wheel 
the operator riding on the car locks the wheel and accordingly regu- 
lates the speed of the car. 
Mine sprags must be made of hard, strong wood, for they are 
given rough usage. Dogwood is admirable for the purpose but is 
difficult to obtain. At present much larger quantities of oak, hick- 
ory, and hard maple are used, and there is a tendency to substitute 
iron pipe for wooden sprags. A few small mills scattered through- 
out Pennsylvania and West Virginia still cut mine sprags, however, 
and among the woods used dogwood is always desired. 
Mine rollers are large cylinders placed under mine-car cables to 
keep the cables off the ground. A hard, dense wood is required and 
for this purpose dogwood is very satisfactory. However, at pres- 
ent the cores of black gum and other veneer logs are being used 
largely for mine rollers, and the practice is greatly to be preferred to 
using young dogwood trees. 
QUILLS 
A great many small dogwood squares are used in the manufac- 
ture of quills (fig. 20) for the silk industry. The term " quill " is 
