132 Discussion of Industries 
pulley, with interchangeable bushings. It has certain advan- 
tages generally recognized. The wood is much lighter than 
iron, much less apt to break through high-speed centrifugal 
force, it does much less injury in the event of a break of a 
large fly-wheel and comphes with the insurance and accident 
regulations of many States. On the other hand, the iron 
pulley has some advantages, one of them being that it does not 
warp or twist so much as wood in outdoor places and where 
exposed to extreme moisture. The general class of pulleys and 
conveyors consists of the larger fly-wheels in factory work and 
what are known as “cone pulleys” or graduated steps or 
blocks on which the smaller leather belts are carried. Large 
fly-wheels 20 to 30 feet in diameter and 5 to 9 feet across the 
face are built up with a great deal of care. The lumber enter- 
ing these large wheels must be thoroughly kiln-dried in order 
to hold its shape, and many courses of lumber are necessary to 
build up these wheels which are subjected to great centrifugal 
strains at high speeds. 
Cone pulleys to be really strong and serviceable need to be 
“built-up” also, on a regular raceplate and of very thin 
material. The article thus produced is non-shrinkable and. 
designed to stand the wear and tear of many years. The 
smaller ones generally consist of at least six segments. White 
pine may be used because it takes glue well and holds nails 
without splitting, but in New York hardwoods are preferred. 
Maple will stand very satisfactorily the severe wear and tear 
of the industry. 
Tackle-block shells use a large part of the raw material in 
this industry. They are the hollow forms in which metal strips 
and rollers are placed for lifting heavy weights, their useful- 
ness consisting of their capacity to multiply the pulling power - 
of machinery and animals. Metal has been used extensively 
for the smaller block shells, but in the larger compound tackle 
blocks metal is entirely too heavy. Wood is generally recog- 
nized as the most satisfactory tackle-block shell. 
3irch is the wood reported as used to the greatest extent in 
the manufacture of tackle-block shells, nearly one-half of the 
amount reported having teen devoted to this purpose. Ash 
