No. 14. Lock joint. This is a form of lap joint rarely used. It resists pulling apart, but should be glued on account of shrinkage.
No. 15. Notched joint; used where two pieces cross, and where full halving is not desirable, as in the sketch of pergola.
No. 16. Rabbeted or gained joint.
No. 17. Dado joint.
No. 18. Gained or housed joint.
No. 19. Through mortise and tenon, used in furniture construction and building.
Note—16, 17, 18 are often confused, and are named differently by mechanics. They are used in boxes, and cabinet work.
No. 20. Blind mortise and tenon, same as No. 19, except that the tenon does not go through and is invisible. These two joints may be fastened with glue, and are often strengthened by passing a dowel through at right angles to the tenon. Another method is to make two or more saw cuts in the tenon, and drive wedges into the cuts.
In door construction, where the rails meet the stiles, the tenon is often divided, as shown by the dotted line. The two parts fitted into separate mortises give the appearance of two distinct tenons on the edge of the door.
No. 21. Relished mortise and tenon or door joint, a form used at the corners of doors.