This section is from the book "School Sewing Based On Home Problems", by Ida Robinson Burton, Myron G. Burton. Also available from Amazon: School Sewing Based On Home Problems.
Paragraph 138. The felled seam is a very flat seam made by turning in and hemming, or stitching flat, one overlapping edge of a seam. It is made as follows: Baste and stitch the material with the machine, or sew with the combination stitch, on the wrong side; trim off the raw edges to the width desired, from 3/16" on fine underwear, to 3/8" on tailored skirts. Trim one edge of the seam to within about 1/8" of the stitching; with its raw edge slightly turned under, turn the wider edge over toward the trimmed edge. Baste neatly in place, being careful that the seam lies perfectly flat. See No. 1, Figure 44. Sew in place with fine hemming stitches (Par. 114).
The Stitched Fell.
This seam is made the same as the hemmed fell except that the second edge is stitched as shown in No. 2, Figure 44, instead of being hemmed in place; it is sometimes made on the right side of a garment.
Figure 44.
The felled seam is used any place where a flat seam is desired. It is particularly desirable in under garments, like drawers and combination suits. Any garment which is worn next to the skin should be finished with this seam.
 
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