In this type of joint one piece crosses over the other.
These two ‘bridle joints’ are used when a light frame is needed. for example, a picture frame. One part of the joint fits into the other part and is glued permanently in position.
MORTICE AND TENON JOINTS
These are used when making tables or cabinets and they are very strong when glued together.
DOWELLED MORTICE AND TENON JOINTS
This is another example of a mortice and tenon joint. However, in this example a piece of dowel rod is drilled through the mortice and the tenon. This helps keep the joint together even when it is under great pressure. This is used as a joint on chairs and other pieces of furniture so that the joints do not break apart when extra weight is applied.
THE SECRET HAUNCH MORTICE AND TENON
If the mortice and tenon joint is to used as part of a frame a secret or sloping haunch is used. The tenon does not show on the outer side of the joint and it gives greater gluing area, adding to the overall strength of the joint.
WEDGED MORTICE AND TENON
This is a very strong and attractive joint. The tenon has two slots and when it is pushed into the mortice wedges are tapped into position. The wedges hold the joint together firmly and they also give the joint an interesting look.
See more and photos at http://www.diydoctor.org.uk/projects/timberjoints1.htm