You are here: / / SEM Screws

Sem Screws - Captive Washer Screws

In order to increase the speed and efficiency of your assembly processes, Inserco Fasteners provides a very diverse range of fasteners commonly used in the field of electronics.

SEM screws, also called captive fasteners are fasteners associated with one or more permanently fixed washers.

The washers are installed during the manufacturing process on the screw blank before rolling the thread. As the outer diameter of the thread is greater than the inner diameter of the washers, they cannot separate from the screw.

This design eliminates the need to place the washer(s) on the screw by hand during installation, greatly facilitating the installation and thus gaining in productivity.

Download the Data Sheet

MOUNTING CONSTRAINTS FOR ELECTRONICS APPLICATIONS

– Temperature variations: cause expansion and loosen fasteners
– Vibration: loosens fasteners
Internal: electro-magnetism, motors
External: vehicles, motion
– Pressure on the mounting surface of the part to fasten: expands the material and causes a loss of tension in the assembly

BENEFITS

The pre-assembled fastener has many advantages:
– Guarantees locking and resists loosening
– Facilitates assembly and disassembly (parts are pre-assembled)
– Simplifies stock management and logistics
– Eliminates non-compliance related to improper assembly or missing washers
– Let’s you combine washers without forgetting any on circuits (DC)
– Improves productivity: no need to fit washers prior to assembly
– Improves quality

We supply fasteners that meet ISO, DIN or NFE requirements and we can also produce bespoke products to your drawings.

Photo3-vis-a-rondelle-imperdable
Photo-vis-a-rondelle-imperdable
Photo2-vis-a-rondelle-imperdable

CHARACTERISTICS – SEM SCREWS SPECIALLY MADE

Thread diameter d1 a max. Min. Useful screw length l2² In excess of the lengths stated partial threading l3 Washer dimensions
Hex. / hollow head screws Slotted screws and philips/Pozi screws Washer to DIN 6902 Spring washer to DIN 6904 Split lock washer to DIN 6905 Ribbed washer to DIN 6906 Star washer to DIN 6907 Conical washer to DIN 6908
Shape A Shape B
s d2 s d2 h d2 h d2 h d2 h d2 h d2
M2,5 0,9 5 16 25 0,6 6,5 0,8 8 – – 1,1 4,55 0,8 5,5 1,2 5,5 1 6
M3 1 6 22 25 0,6 7 0,8 9 1,05 8 1,3 5,65 0,8 6 1,2 6 1,2 7
(M3,5) 1,2 7 25 25 0,8 8 0,8 11 1,15 8 1,3 6,1 1 7 1,5 7 1,2 8
M4 1,4 8 25 30 0,8 9 1 12 1,65 9 1,4 6,95 1 8 1,5 8 1,5 9
M5 1,6 10 35 35 1 10 1,6 15 1,75 11 1,7 8,55 1,2 9 1,8 9 1,8 11
M6 2 12 35 35 1,6 12,5 1,6 18 2 12 2,2 11 1,4 11 2,1 11 2 14
sem-screw-plan

CHARACTERISTICS – SEM SCREWS FROM STOCK

Screw standardWasher standardMaterialDiameter
Pan head screw with flat washerDIN 84DIN 6902ACL 4,8 + ZNM3-M5
Pan head screw with spring washerDIN 84DIN 127BCL 4,8 + ZNM3-M4
Rounded head philips screw with flat washerDIN 7985DIN 6902ACL 4,8 + ZNM3-M5
Rounded head screw with ribbed washerISO 7048DIN 6797ACL 4,8 + ZNM3-M4

WIDE RANGE

SEM screws offer a wide range of assembly options. Inserco can meet all your needs by working to your drawings and/or specifications.

TypeStandardMaterial &
Treatment		Diameters /
Dimensions		Combinations
ScrewTH, CS, CHC, CZX, …ISO, DIN, NFE, UNC/
UNF, …		steel, zinc plated
steel, stainless steel,
etc.		M2,5-M6
Washerflat, wave, conical,
star, Grower, CS		DIN 6900 or
non-standard		steel, zinc plated
steel, stainless steel,
etc.		To DIN 6900 or otherflat + wave, flat + Grower,
etc.

WHICH WASHER AND WHY?

Flat washer Used to spread the load for tightening
No lock function		 3m
Toothed washer The teeth have an anti-slackening function
Partially damages the pressure side		 3m
Spring washer Compensates for longitudinal motion due to material expansion or creeping
Assembly tension is maintained		 3m
Dual-function washer Grower (spring + one tooth)
Contact (spring + teeth)		 3m

Quality

All our sites are ISO 9001 certified and our quality systems meet the specific requirements of the automotive and aerospace industries.QAS 9001 Logo