SEMS Screws Grade 8.8 Zinc Plated DIN and ISO Standard with Pre-Assembled Washer for Automotive and Machinery Fastening
SEMS Screws — Regional Names, Grades, Standards & Buyer Tips
SEMS screws (machine screws with pre-assembled or captive washers) cut assembly time, reduce lost washers, and give predictable clamp loads. This short guide explains common names, materials/grades, relevant standards, typical uses and a buyer checklist.
What is a SEMS screw?
A SEMS screw is a machine screw delivered with a washer fixed or retained on the shank. Compared with separate washers, the pre-assembled washer stays with the screw through handling and assembly, reducing picks, drops and rework on the production line.
Regional and industry names
- SEMS screw — common in North America and UK.
- Combination screw — used in many catalogs and listings.
- Captive washer screw / pre-assembled washer screw — descriptive names common in electronics and appliances.
- Chinese: 组合螺钉 — often translated as combination screw.
Standards, materials and grades
SEMS assemblies are specified by referencing the accepted standards for each component:
- Screws: DIN/ISO/JIS/ANSI for head style, drive and thread.
- Washers: flat, spring, or toothed types per DIN/ISO.
- Grades: carbon (4.8, 8.8, 10.9) and stainless (A2-70, A4-70).
- Coatings: zinc plating, zinc-nickel, GEOMET or stainless passivation for corrosion resistance.
Typical applications
Commonly used where speed and repeatability matter:
- Automotive trim, brackets and HVAC assemblies.
- Electronics housings, racks and power supplies.
- Appliances, machinery panels and service covers.
Buyer checklist — what to specify
- Head & drive type (hex, socket, pan, Torx) compatible with your tools.
- Washer stack (flat only, flat+spring, serrated) for vibration control.
- Material/grade and corrosion requirement (test hours if needed).
- Thread form (metric vs UNC/UNF) and tolerance.
- Critical dims: length under head, washer OD/ID, stack order.
- Required documents: material certs, PPAP for automotive projects.