I always make my half sq triangles 1" larger than called for & then square them up to the correct size before sewing to the other squares . For example; if pattern calls for 2&1/2 " HST, cut both sq. 3& 1/2" draw & sew on the diagonal line & then press open , now resize to 2&1/2" It works every time & saves the frustration of working with 7/8" Good luck!!