Machine Design

Captive Nuts

Captive, or self-retained, nuts are multiple-threaded fasteners used on many thin materials. They are good in blind locations, and can generally be attached without damaging finishes.

Captive nuts can be attached in a number of ways, and designers should consider what tools or systems are needed before selecting the fastener.

There are several categories of self-retained nuts. Plate or anchor nuts have mounting lugs which are riveted, welded, or screwed to the part.

Caged nuts use a spring-steel cage that retains a standard nut. The cage may snap into a holder or clip over a panel edge. These nuts come in strips up to 6 ft long for applications requiring fixed nuts in equally spaced sequences.

Clinch nuts have pilot shanks that are clinched or staked onto the parent part through a precut hole.

Other forms have a knurled or lobed base ring that is pressed into the panel, displacing the sheet metal to become self-retaining. Lobed types have a smooth sinusoidal lobe shape with a radius greater than 5% of the nut's nominal thread diameter. Such lobes meet the requirements of MS33588, and do not create stress risers in the parent material. Lobed nuts are available in standard and self-sealing versions.

TAGS: Fasteners
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