I inherited my mother’s quilting supplies. This description comes from Google:

The AccuQuilt GO! Setting Triangles 10" Finished Die (55553) is a specialized quilting tool designed to cut the corner and side setting triangles needed for on-point quilt layouts featuring 10-inch finished blocks.

Product Specifications

According to Sewing Parts Online and AccuQuilt, this die board measures 10" x 24" and requires a matching 10" x 24" cutting mat. It is compatible with the GO! and GO! Big fabric cutters.

Side Triangles:

Cut Size: 14-7/8" W x 7-3/4" H.

Finished Size: 14-3/8" W x 7-1/4" H.

Corner Triangles:

Cut Size: 7-3/4" W x 7-3/4" H.

Finished Size: 7-1/4" x 7-1/4".

Design Features: Includes 1/4" seam allowances and specialized dog-ears to ensure easy alignment and piecing without the need for manual trimming.