Tunnel Shank

Definition and Overview

A tunnel shank is a shank attached by passing sewing thread through an elongated passage on the back of the button. Because no through-holes such as two-hole or four-hole types appear on the front side, it gives a clean look to the design surface. It also features a space under the shank that accommodates fabric thickness.

“Tunnel” is a name derived from the fact that the part through which the thread passes looks tubular or arched. However, the terminology for the shape and the shank cross-section may vary by manufacturer and place of origin, so check the thread direction and shank dimensions on the actual product or specification drawing.

Materials and Structure

The main body of a tunnel shank button is made from a variety of materials, including polyester resin, urea resin, nut, shell, and metal. The shank may be molded integrally with the body or attached as a separate part, and depending on the material and manufacturing method, the strength at the base, weight, and suitability for washing and dry cleaning differ.

Ordinary hole buttons are threaded from the front through the holes, but a tunnel shank uses only the passage on the back side. Whereas a ring shank is a loop-shaped shank made by bending wire, a tunnel shank often has a passage with width, and the way the thread settles and the stability during attachment differ.

• It has a structure that makes sewing holes less visible on the surface.
• The width and height of the opening for threading affect the thickness of the sewing thread and how easily the needle passes through.
• The shank height should be checked against the thickness of the fabric used and the bulk of the buttonhole.

Size Notation and Applications

Button size is expressed by outer diameter in mm, and sometimes by ligne. Ligne is a customary unit used for buttons, and in purchase orders and specifications, clearly stating whether the size is given in ligne or mm helps prevent size mix-ups. The shank height and the internal dimensions of the tunnel also need to be checked separately.

It is used for jackets, coats, dresses, blouses, and similar items where the decorative quality of the surface is to be emphasized. For heavy fabrics, a button with moderate shank height fits into the buttonhole more easily, while for lightweight fabrics, a shank that is too high can make the button appear to stand away from the garment, so selection should match the fabric thickness and the construction of the front opening.

Attachment Method and Handling Precautions

When sewing on the button, thread is passed through the tunnel, and if necessary, a thread shank is made so the button does not sit too tightly against the fabric. A thread shank is a treatment that creates a thread stem between the button and the fabric. Considering the thickness needed to pass through the buttonhole, check the shank direction, sewing thread color, and attachment strength in a trial run before mass production.

Resistance to washing, dry cleaning, and ironing cannot be judged by the shank shape alone; it depends on the material of the button body and surface treatments such as dyeing or plating. Strong impact may cause the shank to crack, deform, or come off. Do not apply a hot iron directly; follow the product label and the handling conditions for accessories.

• In washing tests, check for cracking, chipping, discoloration, changes in gloss, and looseness of the shank.
• For dry cleaning, confirm in advance whether the material and surface treatment are suitable for the solvent.
• When pressing, consider using a pressing cloth or a button guard so pressure does not concentrate on the button.

Differences from Similar Terms

Shank button is a broad term for any button with a shank on the back through which thread is passed. A tunnel shank is one type of such a shank, characterized by its tubular or bridge-like passage. Therefore, a tunnel shank is included in shank buttons, but not all shank buttons are tunnel shanks.

A ring shank refers to a loop-shaped shank made mainly from metal wire and similar materials. A parachute shank may refer to a shank shape that rises from multiple support points. Do not decide material or strength from the name alone; check the attachment method, the orientation of the passage, and compatibility with the buttonhole before use.

Frequently Asked Questions

Can tunnel shank buttons be attached with a sewing machine?

Whether this is possible depends on the width of the passage, the shank height, the stability of the button, and the specifications of the button-sewing machine being used. Make sure the needle and thread pass properly through the tunnel and that the button does not rotate or tilt after sewing. In mass production, it is important to conduct sewing tests with the actual machine.

Is thread shanking necessary for tunnel shank buttons?

For heavy fabrics, overlapping front openings, or bulky buttonholes, thread shanking may be used to create the necessary clearance between the button and the fabric. On the other hand, if the thread shank is too large on lightweight fabrics, the button will stand away from the fabric, so adjust it according to fabric thickness, shank height, and buttonhole thickness.

Are tunnel shanks and ring shanks the same?

Both are shank-button shapes that make the sewing holes less visible on the surface, but they do not mean the same thing. A tunnel shank generally refers to a tubular or bridge-like passage, while a ring shank generally refers to a loop that rises up. Because the terminology can vary in actual use, check the drawing or the physical sample.