This is an exploded view of a brace tenon and its mortise. This brace is centered on the tie beam (which has been rotated so you can see into the mortise.)
And the brace tenon is centered on the brace.
This type of mortise and tenon joint is a little more complex to cut as the shoulders of the mortise have to match and the shoulders of the brace have to match on either side of the tenon.
The brace is a 4×6 brace and the tenon is 2″ thick.
If your timbers are planed then this type of joint is easier to cut.
Use template with Router on Knee Brace with Centred Tenon? for 16’x20′ project so explain me about it?
You can if your timbers are planed on all four side and the dimensions are true.
With planed timbers the surface that the mortise housing is cut into is flat and 90° to the adjacent faces. The router can be set to the correct depth and it will work if you are accurate with your layout.
Trying to do it with rough sawn timbers will be a challenge as the timbers may not have faces that are truly square to one another.
The measuring point for the leg of the triangle is difficult to cut accurately in rough sawn timbers with a router and template because the timbers surfaces may not be 90° to each other.
Jim Rogers