Hex Socket Button Head Screw

We make hex socket button head screws with a captive washer, in carbon steel with an eco green zinc finish, quoting them from M1 to M10. Washer diameter, thickness and freedom to turn are agreed on the drawing, and the first article is fitted on your finished panel.

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ISO 9001:2015 · Manufacturing since 1998 · 8,678+ customers · 89 countries and regions

Made to order – there is no stock catalogue. Each part is produced to your drawing, and production starts after drawing review and first-article approval.

What Hex Socket Button Head Screws Are

Hex socket button head screws are screws with a low domed head, a hexagon socket drive and a captive flat washer held under the head. The part recorded here is carbon steel with an eco green zinc finish, quoted from M1 to M10 with lengths made to the drawing.

Button head. A low dome with a rounded rim, softer than a cap head and smaller in bearing area.

Captive washer. A flat washer that is loose enough to turn but too large to come off, so one part does the work of two.

Hexagon socket. An internal hexagon driven by an Allen key, with the depth that the domed head allows.

Eco green zinc. A trivalent zinc finish, free of hexavalent chromium, with a green-blue tone that varies slightly between batches.

These are the screws that end up on covers, guards, cycle components and equipment panels: the head is meant to look finished rather than industrial, the washer keeps the head from digging into paint, and the socket lets one hand drive it from above.

The Washer Is Part of the Part

A button head has a rounded rim and a small flat area underneath. That is deliberate for appearance and for comfort, but it is poor at spreading load: the contact patch is narrow, and on a painted or soft panel the head marks the surface before the joint is tight. The captive washer fixes that by adding a flat bearing face without changing the head.

The washer has to be captive in a specific way. It must turn freely, so the head can rotate against it while the washer stays still and does not score the panel; it must not come off, so the assembly cannot lose it; and it must sit flat, so the load goes through the washer rather than through the rim. A washer that is pinched under the head looks correct and behaves like a solid flange.

The gap between the washer bore and the shank decides how it behaves. Too tight and the washer binds and turns with the screw, scoring the panel; too loose and it rattles, sits off-centre and loads one side of the head. On a small screw the difference is a few hundredths of a millimetre, which is why the washer is matched to the shank rather than selected by nominal size.

The finish then adds a complication. Zinc is deposited everywhere, including between the washer and the head, and a coating that bridges that gap welds the two together. That is why the parts are plated assembled and then worked, or plated before assembly with the washer free to move: the second approach costs a step and keeps the washer turning.

None of this makes the screw stronger. The button head still has a shallow socket and a small head; the washer only restores the bearing face that a cap head has by design. Which is the honest way to specify it: a button head screw with a washer is an appearance choice that has been made serviceable, not a high-strength fastener.

Sizes, Head and Washer

The recorded range is M1 to M10, with lengths made to the drawing. Custom lengths up to 2,000 mm are subject to the drawing submission and DFM review. The quotation for a hex socket button head screw carries the head diameter and height, the socket size and depth, the washer diameter and thickness, the thread pitch and the overall length.

Washer diameter is the dimension that decides whether the joint marks the panel, and it is usually specified as a multiple of the head diameter rather than as an absolute value. Thickness decides how much the washer can spread the load before it dishes, and on a thin washer that dishes the head goes through the middle of the deform.

Freedom to turn is the tolerance that never appears on a drawing and always matters in assembly. It is agreed as a behaviour rather than a dimension: the washer turns under light finger pressure and does not fall off when the screw is shaken. That is how it is checked on the first article.

Socket depth is limited by head height, as on any low head. On a button head the dome leaves a little more depth at the centre than the rim suggests, and the key has to reach the floor of the hexagon rather than the crown of the dome.

What a Button Head SEMS Screw Gives and Costs

Four properties decide a hex socket button head screw, and each one carries a cost:

The value is assembly speed and appearance together. A worker picks up one hex socket button head screw, drives it, and the washer is already there and in the right place. On a line that fits hundreds of covers a day, that is the saving that pays for the part.

The cost is that the washer becomes a quality item in its own right. If it binds, the screw scores the panel as it tightens; if it sits off-centre, the load is uneven; if the zinc bridges it, the assembly loses the benefit that was designed in.

Eco Green Zinc and the Washer Gap

The recorded finish is eco green zinc, a trivalent zinc passivate. It protects by sacrificial action, so a scratch in the coating does not start a rust ring, and it is free of hexavalent chromium, which is what makes it acceptable for export markets that restrict it.

Finish Options for Hex Socket Button Head Screws

On a SEMS part the finish has one extra requirement: it has to reach under the washer and it must not bond the washer to the head. The batch is worked after plating, and a sample from each lot is checked by hand for freedom of the washer before the parts are packed.

Colour is the other variable. A trivalent green passivate varies slightly with bath age and part geometry, and on a visible head the difference between two batches is noticeable when they are side by side on the same panel. Where a run is split across lots, the colour standard is kept with the inspection record.

Where Hex Socket Button Head Screws Are Used

Three settings where a low head and a captive washer are both wanted:

Why Shi Shi Tong for Hex Socket Button Head Screws

Four reasons that matter on a washer-equipped part, each tied to something the drawing has to prove:

How Hex Socket Button Head Screws Are Made

These screws are headed on single-die machines that form the button head in one stroke, broached with a hexagonal punch, thread rolled, assembled with the captive washer, and zinc plated as a batch. The first part of every run is measured on head diameter and height, socket size and depth, washer diameter and thickness, thread and length.

Forming the dome and the washer seat is one operation. The punch has to leave a flat annulus under the dome that the washer can bear on, and a radius at the rim that reads as a button rather than a cap. If the annulus is too narrow the washer rocks; if the radius is too tight the rim chips when the head of a hex socket button head screw is polished or plated.

Fitting the washer is the step that decides whether the part works. The washer is pressed over the shank after the thread is rolled, and the head is formed slightly oversize so the washer cannot pass it. The press depth is set so the washer is free but not loose, and the setting is checked by shaking a sample rather than by measuring the gap.

Plating comes after assembly, and the batch is worked afterwards. Each part is turned under a soft pad so the washer moves against the head and the zinc that bridged the gap is broken, without removing the coating from the bearing face. It is a small step that is easy to skip and easy to see on the assembly line when it has been.

Inspection: Head, Socket, Washer and Plate

What decides whether hex socket button head screws pass is the head, the socket, the washer and the plating. The inspection agreement covers those, and the criteria come from the drawing.

Head height and socket on the projector	Thread and start checked
Core hardness checked	Salt-spray testing of the zinc layer

Head height is measured with the socket depth, because the dome and the hexagon come out of the same stroke. The washer is measured for diameter and thickness, and its freedom is checked by hand on a sample from every lot: it must turn under light pressure and must not come off.

Plating coverage is checked under the washer on a sample part that has been taken apart. That is the only way to see whether the zinc reached the annulus, and it is the check that predicts a washer that will rattle or bind in service.

A sample from every batch is driven into the customer panel at the line torque and removed. That cycle shows a washer that rotates with the screw and marks the paint, a head that sits proud, or a socket that has started to mark, and on a hex socket button head screw it is the check that predicts what the assembly line will see.

Certificates and Material Documentation

Every batch is traceable to the wire it was made from and to the plating lot that finished it. The grade and heat number appear on the material certificate supplied with the parts, and the inspection records follow the criteria agreed on the drawing.

ISO 9001:2015	RoHS test report
Registered trademark	Patent: security screw and driver

With each shipment we supply the material certificate, the inspection record for the dimensions on the drawing including the washer, and the plating thickness and RoHS reports. The documents carry the drawing revision and the batch number, so a repeat order keeps the same finish and the same washer feel.

Customers and Projects

More than 8,678 customers in 89 countries and regions have ordered from Shi Shi Tong; 87% of orders come from repeat customers and 56% through referrals. Most projects follow the same route: drawing review, first-article approval, then batches checked against that sample. On a SEMS part the first article is fitted on the customer finished panel, because the washer only shows what it does in the surface it presses. Buyers visit during the process to review samples.

Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the headers and the plating line can be seen on the day the parts run.

Customer group visit – sample review	Customer group visit – process discussion	Customer group visit – factory tour
Customer visit – project kick-off	Danish customer – drawing review	Industry exhibition – meeting customers

Related Products and Guides

Technical Guides

Hex Socket Screw Specification Table How socket size and head height line up across the diameter range. Read the guide

Plating Requirements for Screw Surface Treatment What a plating specification has to state so the finish survives assembly. Read the guide

Products

Pan Head Screw With Washer The same captive washer under a pan head. Pan Head Screw With Washer	Pan Head Sems Screw The SEMS construction described on its own page. Pan Head Sems Screw	Socket Head Cap Screw The standard cap head without a washer. Socket Head Cap Screw
Low Profile Socket Head Screws A socket head with less height. Low Profile Socket Head Screws	Pan Head Socket Screw A socket drive in a rounded head. Pan Head Socket Screw	Cap Screw Socket Head Screw The machine-thread socket head family. Cap Screw Socket Head Screw

Hex Socket Button Head Screw FAQ

Order Hex Socket Button Head Screws

How a button head SEMS project runs from drawing to repeat delivery:

Each step is confirmed with you before the next one starts; the drawing revision from the first article is what repeat orders are checked against.