I've seen others here use these, both shop made and commercial versions. My last set finally got tired and went to that big burn pile in the sky. When making a new batch I thought I'd make enough to take dad a set. I take a piece of hardwood stock about 1-1/2" square and 8-1/4" long and rip it at a 45* angle on the bandsaw to create two long triangle shaped block. I glue these to a scrap of 1/4" BB ply.
Once the glue is dry I rip them into 1-1/4" wide strips. Then I crosscut them into two equal lengths.
They are made to assist in gluing 45* miters but, the example gives you the idea even though it lacks the mitered meeting points.
Overall length is just shy of 7". The important dimension is the "tail" that should be at least 4-1/2" long so that you can clamp without your clamps running into each other.