Step-by-step processing of codpiece and zipper in women's trousers

Processing the codpiece (zipper with a slope) in trousers is one of the key stages that determines the appearance and fit balance of the front half of the product. Errors in this area lead to distortions, bristling of the fabric and skewed stitching. In this article we will analyze in detail the step-by-step technology of sewing a classic codpiece with a slope, which guarantees perfect smoothness and no creases. This technique is ideally applicable when sewing classic pattern of women's trousers BG001 or men's models.

Anatomy of a knot: one-piece codpiece, slope and cut-off facing

A classic trouser fastener consists of two main elements that protect the body from contact with the zipper teeth and ensure a tight fit:

• Codpiece (set): Allowance along the middle seam of the right front half of the trousers (or left in men's models), on which the finishing curly stitch is performed.
• Slope: A separate piece of main fabric with a fold, placed under the zipper on the left side to protect clothes from snagging.

Step 1. Marking, duplicating and preparing parts

The evenness of the entire structure depends on the accuracy of the preparatory work.

1. Duplication: Duplicate the codpiece allowance on the right front half and the place where the zipper is stitched on the left half with a thin thread duplicator. This will prevent the fabric from stretching during use.
2. Preparing the slope: Fold the slope piece in half lengthwise with the right side inward, stitch the lower cut corner, turn it inside out, straighten the corner and steam it. Overlock the long open cut with a serger.
3. Marking: Draw a reference line for the middle of the front and the bottom point of the fastener (notch at the end of the zipper).

Step 2. Processing the one-piece codpiece and sewing in the zipper

Iron the codpiece seam allowance on the right front half inside out exactly along the line of the middle front.

Attach the trouser zipper (with metal or plastic teeth) with the tape to the folded seam allowance of the codpiece, right side down. The edge of the teeth should be located at a distance of 5–7 mm from the bend line. Sew the right zipper tape to the codpiece seam allowance without catching the main part of the trousers.

Step 3. Connecting to the slope and fixing the left side

• Press the middle seam allowance on the left front half inside out, 2mm short of the mid-front line (to create a technical step that hides the zipper).
• Place the prepared edge and loose zipper tape under the ironed edge of the left half.
• Sew a stitch to the edge (1-2 mm from the fold), simultaneously connecting the left half of the trousers, the zipper tape and the hem.

Step 5. Stitching the finishing frame and installing bartacks

Close the fastener and pin the front halves of the trousers along the center front line.

On the front side, using a cardboard template, apply a line of finishing stitching for the codpiece (the stitching width is usually 3–3.5 cm). Important rule: before stitching, move the free slope to the side so as not to stitch it to the front half!

Place a finishing stitch from top to bottom, smoothly rounding it towards the middle seam. Return the hem to its original position and place a tight, short zigzag bartack at the bottom of the codpiece, gripping the hem to prevent tearing of the fabric when putting it on.

Tailor's advice
To ensure that the curly stitching of the codpiece is perfectly smooth and without “waves,” use a rigid template made of thick cardboard. Secure it with masking tape to the right side of the fabric and stitch close to the edge of the cardboard using the topstitch foot. And proven ready-made patterns from our catalog will help you sew trousers with an impeccable balance of front and back halves.

Frequently asked questions (FAQ)

How long should I take a zipper for trousers?
The length of the trouser zipper should be 1.5–2 cm longer than the marked length of the entrance to the fastener. The excess spiral on top is easily removed when sewing the belt.

Why does the codpiece puff up and go in waves after assembly?
Buckling occurs due to the lack of duplication of allowances with adhesive tape or due to excessive thread tension when performing the finishing stitch. Always reduce presser foot pressure when working on complex knots.

In which direction is the codpiece processed in women's and men's trousers?
In women's trousers, the classic codpiece is wrapped from right to left (finishing stitching on the right half), in men's trousers - from left to right (for example, how is the pattern of men's trousers BM002 designed). However, in modern unisex fashion, this rule is often advisory in nature.

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