Pan Head Three-Piece SEMS Screws
Cross Recessed Machine Screws with Captive Spring Lock Washer & Flat Washer
Pan Head Three-Piece SEMS Screws combine a cross-recessed machine screw, one captive single-coil spring lock washer and one captive flat washer into a ready-to-install fastening assembly. The retained washer stack reduces loose-component handling while preserving controlled washer rotation and axial movement.
Product Overview
This page covers one specific three-component assembly only: a cross-recessed pan head machine screw, one spring lock washer directly beneath the head and one plain flat washer beneath the spring washer. All three components remain together during packaging, production and maintenance.
The flat washer increases bearing contact and protects the mating surface, while the split single-coil spring washer supplies an elastic contact element. Joint security still depends on clamp load, joint stiffness, surfaces, installation and application; no universal vibration-proof claim is made.
For purchasing, specify diameter, pitch, length, recess type, screw material, spring-washer material, flat-washer material, washer OD and thickness, finish, standard or drawing, mating thread, application and quantity.
Technical Specifications
Three-Piece Captive Structure, Washer Stack & Thread Engagement
Material, Size & Finish Options
Washer Dimensions & OEM Manufacturing
Diameter, pitch, length, head diameter and height, cross recess and thread length.
Spring-washer OD, thickness, free height, material and geometry; flat-washer OD, ID, thickness and material.
Specify screw, spring-washer and flat-washer materials separately, plus size, finish, standard/drawing, application, quantity and sample.
Inner bags, small boxes, bulk packs, export cartons, pallets, customer labels, part numbers and authorized private label.
Captive Assembly & Quality Inspection
Inspection verifies component count, order, washer split/height/flatness, rolled thread, controlled movement and retention during normal handling. Materials are verified separately for screw, spring washer and flat washer. Functional testing may use a tapped hole, nut, weld nut, rivet nut or clinch nut; no universal torque, clamp-load or vibration value is invented.
Applications
Captive screw, spring washer and flat washer assemblies for repeatable OEM machine-thread fastening.
Captive washers simplify covers, panels and internal-bracket assembly.
Predefined washer stacks for removable machine-threaded guards and panels.
One handled component for brackets, housings and mechanical assemblies.
M3–M6 configurations for repetitive chassis and equipment production.
Standard or drawing-based supply with specified component materials and packaging.
Frequently Asked Questions
What is a Three-Piece SEMS Screw?
It combines one machine screw, one captive spring lock washer and one captive flat washer into a single pre-assembled fastener.
What is the correct washer order?
The standard order is pan head screw, spring lock washer and then flat washer, with the flat washer contacting the mating component.
Are the washers welded to the screw?
No. In a common process the washers are installed before final thread rolling; the larger finished thread retains them while permitting controlled movement.
What standard can be used?
GB/T 9074.4 is a direct reference where dimensions conform. DIN 6900-3 and ISO 10644 do not independently define this complete spring-plus-flat-washer stack, so custom variants are supplied to drawing.
Can Three-Piece SEMS Screws be supplied in stainless steel?
Yes. VALTOR can supply 304/A2 and 316/A4 assemblies as well as carbon steel. Specify the material of all three components independently.
Related Products
Share size, pitch, length, recess, screw and washer materials, washer dimensions, finish, standard/drawing and quantity with VALTOR.