Shafting is nearly always cylindrical and made of wrought iron or steel.
Cast iron is rarely used for shafting.
_Axles_ are shafts which are subjected to bending without twisting.
The parts of a shaft or axle which rest upon the bearings or supports
are called _journals_, _pivots_, or _collars_.
In journals the supporting pressure is at right angles to the axis of
the shaft, while in pivots and collars the pressure is parallel to that
axis.
Shafts may be solid or hollow. Hollow shafts are stronger than solid
shafts for the same weight of material. Thus a hollow shaft having an
external diameter of 10-1/4 inches and an internal diameter of 7 inches
would have about the same weight as a solid shaft of the same material
7-1/2 inches in diameter, but the former would have about double the
strength of the latter. Hollow shafts are also stiffer and yield less to
bending action than solid shafts, which in some cases, as in propeller
shafts, is an objection.