Jessem Stainless Steel Dowel jig Spacer Bottom.

1/4 " Jess Em Jig 

The stainless steel Jess Em doweling jig (thin) are good jigs.  In some situations, the jig is too thin to locate on a dowel to drill mating holes.  This spacer shims up the jig so you can locate on the dowel.  This shim will work when putting a  ¼" dowel centered in 1x material on the edge.  Then locating that pin in the side of another board.  This piece is used when you don't use the fence. It was designed to be used with 

https://www.printables.com/model/1202180-jessem-dowel-jig-top-spacer

I used ¼ x 20 x 1" hex bolts, the head has a press fit in the plate .   Then you can use wing nuts or knobs to hold it all together.

You can get the latest FreeCAD model here. 

https://gitlab.com/public_outlaws42/CAD_Files/freecad/-/tree/main/Tools/Dowel-Pin-Jig?ref_type=heads