These frame alignment jig are used to square your frame on your decks to you're desired deck overhang amount. They come in a set which includes 4 corner jigs that have a set "overhang". They jigs are all connected by elastic so that they can be used on saw horses or on the bench and not worry about the jigs falling off during use as well as staying tight while in use. The jigs have a 3/4" slot to fit over your deck material.
These jigs are double sided. They have different overhang dimensions on opposite sides. The final product will have the dimension printed into the corresponding face.