USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 2/TASK 1
HAND SCREW CLAMP, EXPLODED VIEW.
Jacks are used to raise or lower work and heavy loads
short distances. Some jacks are used for pushing and pulling operations, or
for spreading and clamping.
b. Types of Jacks. Jacks are available in capacities from 1 1/2 to 100
tons. Small capacity jacks are operated through a rack bar or screw, those
of large capacity are usually operated hydraulically.
(1) Screw Jacks. The vertical screw jack (figure 48 on page 66) is
operated by hand through a collapsible handle which is inserted in a socket.
The screw moves up or down, depending on the direction of rotation in which
the handle is turned.
Some screw jacks are equipped with a ratchet for
automatic lowering. Mechanical screw jacks are issued in several capacities