At 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.
Fig. 364.—Wall Plugs, Four Varieties.
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 . 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. 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; one plate is let flush into the upper piece and the other plate into the lower piece.
Battening .—A good method of joining cross battens to drawing boards and other wide surfaces is shown here. After boring for the screws, slots are cut so as to allow the screws to move along the slots when shrinkage takes place. In a similar method is applied to secure the drawer bottom to the drawer back. If shrinkage takes place in the drawer bottom and it leaves the groove in the drawer front, the screws are slackened, the drawer bottom is knocked up into the groove, and the screws again inserted. For drawing boards, etc., specially made elliptical-shaped slotted brass socket cups are made to receive the screw heads.