8. Tools

Drills, countersinks, counterbores, thread taps, threading dies

There are various kinds of drills, 60° included angle countersinks, cutting dies, serial taps and nut taps for producing through bores and tapped holes. Threading dies are preferred for re-threading screws or threaded bolts.

Figure 23. Drills, countersinks, thread-tap, threading die

Die stock

There are various die stocks for larger ISO metric threads (12 mm diameter and more) for cutting thread in bolts and die stocks for Whitworth pipe thread for the direct joining of pipes.

Figure 24. Die stock

Screw drivers

Screw drivers are used for tightening or screws with a slot across or intersecting slots. Angular designs of screw drivers are known for screws to which access is difficult.

If between the blade and the slot there is a wide clearance, do not use the screw driver. The tolerance between the blade thickness and the slot should be close. The blade width should be marginally smaller than the diameter of the screw head.

Figure 25. Screw driver

Open ended wrenches

There are open ended wrenches of different standard sizes for tightening and loosening hexagon head bolts, screws and nuts. The lengths of open end wrenches are such that the ratio of the median force applied by human arm and nominal thread diameter does not exceed the permissible shearing stress produced when tightening a bolt, screw or nut.

Never use a piece of tube to extend the length of an open ended wrench in a attempt to apply a higher tightening force. The prestress in the joint will be too high.

Nominal thread diameter	M4	M5	M6	M8	M10	M12	M16	M20
Dimension across jaws (mm)	7	8	10	13	17	19	24	30

Figure 26. Open ended wrench

Ring spanners

There are cranked and flat types of ring spanners of different sizes for the tightening and loosening of hexagon head bolts, screws and nuts of higher strength specifications.

Figure 27. Ring spanner

Box spanners

There are box spanners of different sizes for use on hexagon head bolts, screws and nuts where these are accessible only in the axial direction.

Figure 28. Box spanner

Hexagon pin-type wrenches

There are hexagon pin-type wrenches of different sizes for the tightening and loosening of hexagonal socket head screws.

Figure 29. Hexagon pin-type wrench

Adjustable wrenches

Adjustable wrenches are used on hexagon head bolts, screws and nuts where there are different head sizes and no sets of open ended wrenches are available.

Adjustable wrenches replace certain size ranges of open ended wrenches, but they are heavier and less handy.

Figure 30. Adjustable wrench

Torque spanners

Several types of torque spanners are available. They are used where high-strength bolted or screwed joints are required to have a specific torque (tightening torque) or where there are several bolted or screwed joints on one component part and their prestressing is to be the same. The torque can be read at a dial during tightening.

Figure 31. Torque spanner

Electrically actuated wrenches

Electrically actuated wrenches are used in industrial volume production. Various tools can be used on electrically actuated wrenches to tighten or loosen different types of bolts, screws and nuts. Electrically actuated wrenches may be adjustable for torque.

Figure 32. Electrically actuated wrench

What may happen when the blade of a screw driver is too narrow?
______________________________
______________________________
______________________________

What may happen when an extension is used on the open ended wrench for tightening a threaded joint?
______________________________
______________________________
______________________________

Name applications of the torque spanner.
______________________________
______________________________
______________________________