Here are some tips for stitching leather patches for hats together:

Use a matching thread.

Choose waxed thread, cotton thread or synthetic thread that closely matches the color of the leather. This will make the stitching less visible.

Awl punch holes at an angle.

When punching holes for stitching, awl the holes at a slight angle across the seam for the strongest stitch. Straight holes can pull out easier.

Use small stitches.

For patching leather hats, use stitches that are 3-6mm (1/8-1/4 inch) apart. Smaller stitches will provide a stronger, less visible seam.

Double stitch edges.

Place two rows of stitching close together along the edges and corners of the patches for extra strength. This prevents tearing.

whip stitch edges.

In addition to stitching the main seams, whip stitch around the outer edges and sides of the patches. This secures the edges down and hides any raw edges.

Pound stitches tight.

As you sew the patches together, use a stitching mallet or hammer to pound the stitches tight. Pounding the stitches tight makes them lie flat and hold the patches securely together.

Reinforce stitching.

For stress points like corners, apply stitching glue, stitch reinforcing patches, or apply animal glues to the stitching. This prevents tearing at corners and seams.

Tooling edges (optional).

If desired, you can tool or shape the edges of the leather patches using leather punches, knives, chisels or sandpaper. Tooled edges will have a more finished look and prevent fraying.

Apply sealant (optional).

A coat of sealant, especially on the stitching and edges, helps protect the leather from water damage, UV damage and wear and tear. Some good options for leathers include mink oil, neatsfoot oil or acrylic sealers.

Round edges of exposed seams.

If there are any seams on the surface of the hat, you can carefully round them over with fine-grit sandpaper to minimize their appearance. Rounding exposed seams provides a smoother look.