The object of this form is to weaken the mortised member as little as possible but at the same time to increase the strength of the tenon.

It is used in joining tail beams to headers in floor framing.
_No.41.A double mortise-and-tenon_, Fig.

267, consists of two tenons side by side in one piece fitting into two corresponding mortises.

It is used in joinery, as in door-frames, but not in carpentry.
_No.42.A haunched mortise-and-tenon_, Fig.

267, is made by cutting away part of the tenon so that that part of it will be much shorter than the rest.