Tel：
+86 13143444311
Email：sst@szsst88.com
Fax：+0086-755-27322278
Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Type:Captive Thumb Screw
Materials:stainless steel
Surface treatment:plain
Head Type:cap head
Drive:Phillips + Knurl
Thread:Half Machine Thread
Retention:Shoulder
Forming:Turned
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:222
We turn captive thumb screws from stainless bar with a knurled cylindrical head, a cross recess and a half machine thread, retaining the screw in the panel so it cannot be lost. Retention diameter, travel, thread and grade come from your drawing, and the first article is fitted and cycled in your 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.
A captive thumb screw is a panel fastener that stays with the panel when it is unscrewed, so it cannot be lost, and that can be turned by hand as well as with a driver. The recorded item is stainless, turned from bar, with a knurled cylinder head, a cross recess and a half machine thread, quoted from M1 to M14 with Number 222.
Captive by the shank. The screw is retained rather than loose: a plain length under the head passes through the panel, and a shoulder, a ring or a swaged sleeve on that length keeps it from coming out while letting it turn and travel.
Knurled cylinder head. A straight knurl on the side of a cylindrical head, for fingers. On a captive screw the knurl matters more than usual, because the whole point is that the fixing can be opened without a tool.
Cross recess. A Phillips recess in the head, so the same screw can be given a final torque with a driver where the joint needs one. The knurl starts it, the driver finishes it.
Half machine thread. Thread from the point to a defined position, with the plain shank above it. On this part the plain shank is the retention zone, which is why the thread length is short relative to the screw.
On an ordinary screw the plain shank is the part that passes a clearance hole. On a captive thumb screw it is the mechanism: the shank is the surface the panel and the retainer work against, and its diameter and length decide whether the screw stays put, travels far enough and turns freely.
On captive thumb screws the travel is the dimension that is usually missed. A captive screw has to back out far enough to clear the thread in the part below, and no further, or the head lifts off the panel face and the retainer carries the load. That travel is set by the distance between the retainer and the start of the thread, and it is quoted on the drawing as a length, not left to the retainer.
Because the part is turned from bar, the retention features can be cut rather than formed. A turned shoulder, a groove for a snap ring or a step for a swaged sleeve are all normal on a turned screw and all impossible or difficult on a headed one, which is why captive screws are usually turned.
On captive thumb screws the head carries two drives because the joint needs both. The knurl turns the screw by hand for the length of its travel and for a light clamp; the cross takes the final torque where the joint has a defined value. A captive screw with a knurl only is fine for a thumb-tight joint; with a cross as well it can be specified for a joint that is torqued.
Captive thumb screws are passivated after turning. It is the finish as much as the material: on a part that is handled every time the panel is opened, a coating would wear at the knurl and in the cross first, and both are exactly where the fingers and the driver go.
The family is quoted from M1 to M14, with M1, M2, M3, M4, M5, M6, M7, M8, M9, M10 and M14 in the recorded range. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission; on captive thumb screws the retention length and the travel are quoted with the thread, because they decide how the screw behaves in the panel.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Knurled cylinder with a cross | Diameter, height, knurl and recess |
| Retention | Shoulder, groove or step on the shank | Diameter and position, checked on the section |
| Travel | Length the screw can back out | Distance from the retainer to the thread start |
| Thread | Machine thread, partial | Pitch and length, gauged per batch |
| Finish | Plain stainless, passivated | Surface condition and film |
| Length | Overall, and thread length from the end | Measured on the shop plate |
The retention diameter is the dimension that decides whether the part works at all. Too large and the screw will not enter the panel; too small and the retainer pulls through under the first pull. On a turned part it is a single diameter, so it is held tightly and checked on the section of the first article.
Thread length is quoted from the end, and travel from the retainer to the thread start. The two together define how much thread engages when the screw is fully down, which on a captive fastener is the whole of its working length.
Three features define captive thumb screws — the knurled head, the cross recess and the half thread — and the retention is what the customer is buying. Different retainers suit different panels, and the choice is usually made with the panel rather than after it.
| Retention method | How it works | Where it fits | What it costs |
|---|---|---|---|
| Turned shoulder | Shoulder bears on the panel, thread below | Turned parts, small panels | A shoulder diameter to hold |
| Snap ring groove | A ring on the shank stops against the panel | Where the panel is thin | One more part to assemble |
| Swaged sleeve | A sleeve is pressed into the panel | Sheet metal, high volume | A panel operation |
| Threaded retainer | A nut on the shank inside the panel | Thicker panels | Access to the inside |
The choice affects the panel as much as the screw. A swaged sleeve needs a hole of a defined size and a press operation; a snap ring needs a groove that is cut on the screw and a ring that is fitted at assembly; a turned shoulder needs nothing on the panel but has to bear on it directly, so the panel face is a bearing surface and is marked by it.
The failure mode follows from the method. A shoulder pulls into a soft panel, a snap ring can be forced off by an impatient pull, and a swaged sleeve can be pulled out of a thin sheet. What none of them tolerate is a screw that is unscrewed past its travel and then pushed sideways, because that loads the retainer in the one direction it was not designed for.
Captive thumb screws are finished plain stainless and passivated. There is no coating, so the knurl keeps the edge that gives it grip and the cross keeps the depth that the bit needs, and neither degrades into a film that wears off.
| Option | How it protects | Effect on knurl and recess | Typical use |
|---|---|---|---|
| Stainless A2, plain | Passive chromium oxide film | None; knurl and recess as cut | Equipment covers and panels |
| Stainless A4, plain | Passive film with molybdenum | None; knurl and recess as cut | Coastal and washdown |
| Nickel plated brass | Hard barrier deposit | A few microns; knurl softened | Visible and conductive |
| Black oxide on steel | Conversion film, oiled | No measurable build | Dark indoor equipment |
| Anodised aluminium | Grown oxide, dyed | A few microns; knurl re-checked | Lightweight colour-coded parts |
On a captive screw the plating argument is the same as on any knurled part, with one addition: the retention shoulder or groove also changes with a coating. A few microns on a shoulder that has to pass a panel hole can turn a free fit into an interference, and the screw then cannot be inserted at all.
Where the joint is washed or exposed, stainless is the finish that survives without maintenance. The knurl stays the same shape and the cross does not fill, which matters because a captive screw is only as good as the last time it was turned.
Three assemblies where a captive thumb screw is the fixing:
| Where it sits | The screw holds a cover or a module that is opened by an engineer without tools, where a lost screw would stop the equipment being closed again. |
| When it goes wrong | A loose screw is dropped inside the instrument, and a missing one leaves the cover unfastened. |
| Why it happens | The joint is serviced often, the cover is small, and no tool is guaranteed. |
| What we control | Retention and travel checked on the first article, knurl and recess tried by hand and by bit. |
| Where it sits | The screw holds an access panel that is removed for inspection, where a dropped fastener is a foreign object risk and the panel must close with the same screws. |
| When it goes wrong | A lost screw in a vehicle becomes a foreign object, and a screw that cannot be reached costs a maintenance delay. |
| Why it happens | The panel is serviced on a schedule, the access is awkward, and the fasteners must stay with the panel. |
| What we control | Retention diameter and travel checked, thread gauged, parts inspected for burrs. |
| Where it sits | The screw holds a guard that is removed for cleaning or adjustment, where speed matters and the hardware has to stay with the machine. |
| When it goes wrong | A dropped screw in a machine is a hazard, and a guard that will not close delays production. |
| Why it happens | The guard is removed daily, the joint is finger-tightened, and the screw must stay put. |
| What we control | Knurl and retention checked, thread gauged, length matched to the guard thickness. |
Four reasons that matter on captive thumb screws, each tied to what the drawing has to prove:
|
Retention and travel reviewed with the panel
The retention diameter, the travel and the panel thickness are reviewed as one set, so a screw that would not enter the hole or would not clear the thread is raised before the bar is cut. Basis: Retention and travel reviewed with the panel. |
Turned retention built into the part
The shoulder, groove or step is turned on the same setting as the thread, so the retention feature and the thread start stay related to one datum. Basis: Retention turned with the thread. |
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Retention checked by fitting
The first article is fitted into the customer panel and worked through its full travel, because the retention only proves itself in the panel. Basis: First article fitted and cycled in the panel. |
First article fixes the setting
The first article fixes the alloy, the program and the knurl; repeat orders are compared against that record. Basis: First article signed off before the batch is released. |
Shi Shi Tong turns these captive thumb screws from stainless bar: the head is turned and the knurl formed, the cross recess is milled, the plain shank is turned to the retention diameter and the shoulder or groove is cut, and the machine thread is produced to the drawing. The parts are passivated and inspected, and the first article is fitted into a sample panel and cycled through its travel.
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The retention shoulder and the thread start have to be turned in a known relation, and that is the setting that decides the travel. Turn the shoulder a little high and the screw does not back out far enough to clear the thread; turn it low and the screw lifts off the panel face before the thread is free. The dimension is held by the program and checked on the first article in the panel.
What decides whether captive thumb screws pass is the retention feature, the travel, the head, the thread and the alloy. The inspection agreement covers those, and the criteria come from the drawing.
Retention and knurl on the projector |
Thread gauged per batch |
Hardness checked against the alloy |
Salt-spray testing of the stainless grade |
The retention is checked on the section for diameter and position, and then by fitting: the first article goes into the customer’s panel, is worked through its travel and is pulled to confirm the retainer holds. A screw that measures correctly and pulls out of the panel is a screw with the shoulder in the wrong place.
The head of a captive thumb screw is checked for diameter, height, knurl depth and recess depth, and the thread is gauged per batch. On a captive screw the knurl is read by hand as well as by gauge, because grip is the function and a shallow knurl that measures inside tolerance still slips.
Every shipment of captive thumb screws is traceable to the bar they were turned from and to the passivation batch. The grade and heat number are recorded 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 batch we supply the material certificate for the bar, the inspection record for the criteria on the drawing and, where it is listed, the third-party report for the grade or the passivation. The documents carry the drawing revision and the batch number, so the paperwork can be matched to the parts.
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 captive thumb screws the first article is fitted into the customer’s panel, because retention is a property of the pair rather than of the screw. Buyers visit during the process to review samples and to see how the parts are turned.
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8,678+
customers served
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87%
of orders from repeat customers
|
56%
of orders through referrals
|
89
countries and regions shipped to
|
Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the lathes and the knurling station 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 |
A shoulder, groove or sleeve on the plain shank stops the screw leaving the panel while letting it turn and travel. It is a property of the screw and the panel together.
Enough to clear the thread in the part below, and no more. Too little and the panel will not come off; too much and the head lifts off the panel face.
The knurl opens and closes the joint by hand; the cross lets a driver apply the final torque where the joint has one. On a thumb-tight joint the knurl alone is enough.
A captive screw is lost only when the retainer fails, and that is a fitting problem rather than a screw problem. The panel hole and the retention diameter are the pair to check.
A2 for general work, A4 where there is chloride. The finish is the alloy, so the grade is the whole corrosion specification.
Head diameter and height, knurl, recess size, retention diameter and position, travel, thread size and length, and the grade.
How a captive thumb screw project runs from drawing to repeat delivery:
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1
Send the drawing and the panel detail
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→ |
2
Retention, travel and thread review
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→ |
3
First article fitted and cycled in your panel
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→ |
4
Batch production and repeat orders
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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.
For a quotation, send the drawing with the head diameter and height, the knurl, the recess size, the retention diameter and position, the travel, the thread size and length, and the panel thickness.
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Head diameter
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Knurl
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Recess size
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Retention
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Travel
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Thread and panel
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Sending a drawing? The form below does not take attachments. Email the PDF, DXF or STEP file to sst@szsst88.com with the part name and quantity in the subject line – the drawing is reviewed and a quotation follows.
+86 13143444311
sst@szsst88.com
