Date Published:Jul. 08. 2016 Date Updated:Jan. 19. 2024

What are Captive Screws? Introduction of the NBK Captive Series

For CE Marking compatibility and measures against contamination

Components that prevent screws from falling off from covers and getting lost

What are Captive Screws?

Captive screw is a screw whose thread part is applied by relief cut to avoid falling out.
The screw is structured to catch on the cover screw hole not to fall out of the cover even when removed from the frame.
NBK has standardized products for fall prevention of machine parts categories, including captive screw.

CE Marking

CE Marking (CE Mark) is a mark demonstrating that the manufacturer is in compliance with the EC Directive for products such as machinery and equipment.
Products that are exported or distributed to EC member states must comply with the EC Directive. Therefore, in order to circulate the products in EU member states, CE Marking is required to demonstrate that they comply with the EC Directive.
According to the "EU Machinery Directive Annex 1" of "Machinery Directive (2006/42/EC)" in the EC Directive, screws that secure a protective cover or inspection cover of equipment and devices must not fall out of the cover when it is removed.

Excerpt from "EU Machinery Directive Annex 1"

1.4.2 Special Requirements for Guards
Item Fixed Guards
Fixed guards must be fixed by systems that can be opened or removed only with tools.
Their fixing systems must remain attached to the guards or to the machinery when the guards are removed.
Where possible, guards must be incapable of remaining in place without their fixings.

1.1.1 Definitions
(f) ‘guard’ means a part of the machinery used specifically to provide protection by means of a physical barrier.

Types and Features of Captive Series

Captive Series(relief-cut treatment)

Captive Screw

The screw is structured to catch on the cover screw hole not to fall out of the cover even when removed from the frame.

Socket Head Cap Captive Screws

Cross Recessed Pan Head Captive Machine Screws

Socket Head Cap Captive Screws with Low Profile

Captive Knobs

Even when the screw is removed from the frame, the captive knob does not fall out of the cover because it catches on the cover screw hole.

Captive Dimple Knobs

Captive Knurled Knobs
KUM-SC(Flat Type)

Captive Pulls

Even if the nut is loosened, as it temporarily remains in the relief cut part, the pull and nut prevent an accidental fall.

For Captive Pull UNMS-SC


For Pull without Captive Mechanism


Captive Pulls

Captive Processing Service products (special screws) are provided with relief cut and fallout prevention functions.
See here for details on the captive processing service >>

Captive Washers

Captive Washers

Captive Washers

Socket Head Cap Captive Screw/Washer Sets

It is a set of captive screw and washer that were introduced above.
The captive screw catches on the cover screw hole to avoid its fall-off and loss even when the washer is damaged.


Hex Socket Head Cap Captive Screw/Captive Washer Sets

Captive Washer for Pull

With a pull mounted, the pull mounting surface is beautifully decorated while pull mounting screw fallout is prevented.

Captive Washer for Pull
LYSC-N-SSC(with Captive Screw)

Clamp Lever with Built-in Washer

Clamp lever with washer built-in. When assembling to equipment, washer assembly is not required, keeping washers from falling out. Three types of washers are now available as standard. Select according to the usage application.

Integrated Spring Washer Type

Washer assembly is not required, preventing washers from falling out. Remove the plain washer to replace the spring washer with a different washer component.


Integrated Plain Washer Type

For reduction of seating surface pressure in materials with low limit surface pressure, such as resin and aluminum parts. Also ideal for ensuring seating surfaces when tightening slotted holes, etc.

【Integrated Flat Washer Type for Slotted Holes】

The pointer engraved on the top surface enables easy position confirmation when tightening slotted holes. The projection on the washer surface prevents the washer from rotating.

Supports special products

We design and manufacture captive screw in accordance with use conditions, including shapes, dimensions, and materials.
Since we can handle large lot production depending on the specifications, feel free to contact our customer service.

Inquiries about special products including captive screws

For others inquiries, please contact us here

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