Product and assembly brief
SEMS identifies a screw supplied with one or more captive washers beneath its head, not a single head shape or universal locking performance. Specify the complete screw-and-washer construction rather than combining a generic screw name with a loose washer size. Final supply scope follows the selected drawing and quotation.
Product forms and reference names
| Choice or field | What to identify |
|---|---|
| Screw with a plain washer | A retained plain washer on a flat-seating screw. For ISO 10644 enquiries, identify the selected edition and full assembly requirements. |
| Screw with a spring washer | Specify the actual spring-washer form, not just a locking label; Bossard BN 1720 is a source-specific pan-head example. |
| Screw with a toothed washer | Identify internal or external teeth and the selected assembly specification. PENCOM lists these as distinct SEMS forms. |
| Screw with two washers | Specify both washers and their order, for example a spring washer and a plain washer; NBK P=3 is a maker-specific arrangement label. |
| Other catalogue or drawing-defined assemblies | Head form, drive and washer geometry can differ. Square-cone and other washer forms are not plain-washer ISO 10644 assemblies merely because they are captive. |
Captive washer is not an integral flange
A captive washer remains a separate component retained on the screw. ISO 10644 describes retained plain washers that cannot be disassembled and are free to rotate. An integral washer-shaped head flange is part of the screw itself. A screw packed with loose washers is also different: state the required retention and washer movement on the specification.
Standard identity and catalogue distinctions
ISO 10644:2009 covers a defined steel metric coarse-thread screw and plain-washer assembly family with flat seating heads; its scope is not every product called SEMS. ISO 10673:2009 identifies small, normal and large plain steel washer series for such assemblies. Spring, toothed, dual-washer, stainless or proprietary constructions need their own applicable specification. These reference identities do not establish FastenerBridge compliance, equivalence or availability.
Head, thread and washer stack selection
Select pan, hex, socket or another specified head and its drive independently from the washer arrangement. Define metric or inch thread, pitch, length datum and usable thread; include the retained-washer stack and unthreaded region on the drawing. Confirm clearance, bearing surface and mating nut or tapped hole for the actual assembly. No generic pilot-hole size, tightening torque or usable engagement is prescribed here.
SEMS versus panel-captive screws and washer nuts
A SEMS washer is retained on its screw; this does not establish that the screw remains captive in a panel when disengaged. Panel-captive hardware uses a separately defined retention interface. A captive-washer nut has an internally threaded nut body, not a headed screw. Keep these three enquiries separate.
Material, finish and functional boundaries
State the screw and each washer material, required properties, finish and inspection documents separately. Captive construction does not by itself guarantee vibration resistance, electrical contact, corrosion life or reuse. Washer selection, joint loading, installation and any required qualification depend on the selected assembly and application.
Specification fields
| Choice or field | What to identify |
|---|---|
| Assembly identity | Selected standard and edition, maker reference or controlled drawing and revision; one or two washers and their order. |
| Screw geometry | Head and drive, thread system, diameter and pitch, length datum, threaded portion, under-head shank and end form. |
| Washer details | Plain, spring, internal/external tooth or other form; bore, outside diameter, thickness/profile, hardness where required and retained movement. |
| Joint interface | Mating nut or tapped hole, bearing surface, clearance, stack thickness and application-specific acceptance requirements. |
| Materials and finish | Screw and washer designations, specified properties, coating/finish and required documentation; no assumed common material. |
| Order controls | Quantity by variant, samples if required, inspection, packing, destination and requested timing for quotation confirmation. |
Common product questions
Are all SEMS screws ISO 10644 assemblies?
No. Identify the actual construction. ISO 10644 addresses a specific steel metric screw and plain-washer family; spring, toothed and proprietary washer arrangements cannot inherit that scope from the SEMS name.
Does a captive spring washer guarantee locking?
No generic locking guarantee is stated. Identify the washer construction and request the selected joint's installation and acceptance requirements.
Is this the same as a panel-captive screw?
No. Retaining a washer on the screw does not establish retention of the screw in the panel. Panel-captive assemblies have a separately specified interface.
Related product choices
- Machine screw head and thread selection
- Socket and internal-drive screw forms
- Panel-captive screws: different retention interface
- Captive-washer nuts: internally threaded body
- Washer families and specification fields
Product references
References checked 10 October 2026 identify structures, not FastenerBridge stock, compliance or brand affiliation. Final requirements follow the selected specification. No normative dimension, load rating or tightening torque is stated.