My son has an old 20pc plastic puzzle that when assembled makes a 4" square. the yellow pcs are different size triangles with half circles sticking out or cut out of some of the sides. It was made by KPI of Minnesota but we want the solution and it seems that the company may be out of business

any chance of getting pics of the puzzle? That would probably help as the description of the puzzle you give may be slightly out of the scope of this discussion forum.