SEMS screw (captive washer)
ASME B18.13; regional DIN washer combinations
Sizes
M2-M8 metric, #2 to 3/8 in
Drive & head
Phillips, slotted, Torx or hex, with a washer trapped under the head
Materials
Zinc plated steel, stainless
Strength / grades
Commercial grade 2 typical; A2 stainless
Hole and pilot guidance
Same hole as the plain screw, but leave room around the head for the washer diameter.
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Where it is used
Appliance and electronics assembly lines
The washer cannot be forgotten or dropped, which speeds up assembly
View sourceWatch out for
- Cheap versions let the washer fall off once it is unscrewed.
- You cannot change washer type later - it is part of the screw.
- The washer adds height, so grip length differs from a plain screw of the same length.