it resembles a miniature corrugated galvanised sheet such
as is used for roofing purposes, with the exception, however, that the
corrugations are divergent instead of being parallel and that one end is
ground down to a cutting edge (see Fig. 363, A). They are made in various
sizes from 1/4 in. to 1 in. in length, whilst in regard to width they are
classed by the number of corrugations and not by their measurement.

[Illustration: Fig. 362.--Jointing Boards.]

[Illustration: Fig. 363.--Jointing a Frame.]

[Illustration: The Use of Saw-edge Corrugated Steel Fasteners.]

To use the fastener no special tools are required; it is simply driven in
with a hammer exactly as though it were a nail; once in position,
however, to get it out is worse than drawing teeth. The corrugations add
to the strength of the device, the wood fibres closing around them, age
and rust but emphasising their grip.

WALL PLUGS.--At Fig. 364 four types of wall plugs are shown: _a_, the
ordinary rectangular tapered wall plug to drive between the joints of the
brickwork; _b_, the circular tapered wall plug as used to plug a wall
after a star-shaped brick drill has been used; _d_, a twisted wall plug
used for similar purposes to the wedge _a_, but considered to be
superior in holding power owing to its twisted formation; _c_ is another
type of wall plug considered to have great tenacity by reason of its
corrugations. Wall plugs are required in nearly all cases where it is
necessary to joint woodwork to brickwork, as, for instance,
heavily-framed silvered mirrors to the walls of shops.

[Illustration: Fig. 364.--Wall Plugs, Four Varieties.]

[Illustration: Fig. 365.--Slot Screwing.]

[Illustration: Fig. 366.--Slot Screwing a Bracket.]

SLOT SCREWING, OR KEYHOLE SCREWING, is a most useful way of joining light
woodwork in such a manner that the fixing method is not exposed to the
eye. A stout screw is inserted to within 3/8 in. of the head, as at Fig.
365. In the adjoining piece a hole is bored with a centre bit and a slot
is cut with an 1/8-in. chisel. The two pieces of timber are placed
together, and by sliding the upper piece forward the screw runs up into
the slot or keyhole and secures the joint. Fig. 366 shows the application
of the joint fixing a shaped bracket to the shaped shelf; the bracket and
shelf are inverted in the illustration to clearly show the method of
jointing. For heavy work special brass plates are obtainable for this
purpose;