of spurs,
discs with sharpened edges.

The _scratch-awl_, Fig. 218, has a long, slender point which is useful
not only for marking lines, but for centering.

[Illustration: Fig. 217. Roller Mortise-Gage.]

The _auger-bit-gage_, Fig. 219, is a convenient tool for measuring the
depth of holes bored, but for ordinary purposes a block of wood sawn
to the proper length thru which a hole is bored, is a satisfactory
substitute.

_Screw- and wire-gages_, Fig. 220, are useful in measuring the lengths
and sizes of screws and wire when fitting or ordering.

The _spirit-level_, and the _plumb-line_ which it has largely
replaced, are in constant use in carpentering, but are rarely needed
in shopwork.

[Illustration: Fig. 218. Scratch-Awl.]

[Illustration: Fig. 219. Auger-Bit-Gage.] _Blackboard compasses_,
_triangles_, etc., are convenient accessories in a woodworking
classroom.

[Illustration: Fig. 220. Screw- and Wire-Gages. a. Screw-Gage. b.
Wire-Gage. c. Twist-Drill-Gage.]

8. SHARPENING TOOLS.

The _grindstone_ for woodworking tools is best when rather fine and
soft. The grinding surface should be straight and never concave. The
stone should run as true as possible. It can be made true by using a
piece of 1" gas pipe as a truing tool held against the stone when run
dry. Power grindstones usually have truing devices attached to them,
Fig. 221. A common form is a hardened steel screw, the thread of
which, in working across the face of the grindstone, as they both
revolve, shears off the face of the stone. The surface should always
be wet when in use both to carry off the particles of stone and steel,
and thus preserve the cutting quality of the stone, and to keep the
tool cool, as otherwise, its temper would be drawn, which would show
by its turning blue. But a grindstone should never stand in water or
it would rot.

It is well to have the waste from the grindstone empty into a
cisternlike box under it, Fig. 221. In this box the sediment will
settle while the water overflows from it into the drain. Without such
a box, the sediment will be carried into and may clog the drain. The
box is to be emptied occasionally, before the sediment overflows.

[Illustration: Fig. 221. Power Grindstone.]

In order that the tool may be ground accurately, there are various
devices for holding it firmly and steadily against the stone. A good
one is shown in Figs. 221 and 222. This device is constructed as
follows: A board A is m