Plain Blocks or Pieced Corners
The easiest corner block to insert into your border is a plain block. The dimensions of your corner blocks are determined by the width of your borders. For instance, if your borders are finished at 4", your corner blocks also will finish at 4". Unfinished measurements will be 4 1/2". This measurement is crucial if you are going to be constructing an actual quilt block for the corner.
For a pieced corner block, you can use a leftover block from your quilt, or piece a smaller version of that block to fit the border width. Something as simple as a Four-Patch or Pinwheel block adds a lot of pizzazz to your quilt. Determine what size of a block to make based on how big your borders are, your piecing skills, and how you want your quilt to look when it’s finished.