Knurled Head Locking Screw

We manufacture knurled head locking screws with a straight-knurled knob, a cone seat, a plain captive neck and a half machine thread, in carbon steel with an eco nickel finish. Knob, cone, neck and thread are taken from your drawing, down to the recorded 16 mm knob and 6 mm neck.

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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 a Knurled Head Locking Screw Is

A knurled head locking screw is a captive thumbscrew: a screw with a knurled knob instead of a conventional head, a cone seat under the knob and a plain neck below the thread that stays in the panel so the screw cannot be lost. The recorded item on this page has a 16.00 mm knob, a 1.60 mm slot, a 6.00 mm plain neck and an M5 × 13.00 mm thread, in carbon steel with an eco nickel finish, with Number 66.

Knob instead of head. A 16 mm cylinder with a straight knurl around the rim. The diameter is what gives the fingers their leverage, and the knurl is what stops them slipping on a plated surface.

Cone seat. Under the knob there is a shallow cone rather than a flat bearing face. It centres the screw in a countersunk panel hole and pulls the panel down evenly, which on a hinged cover also compresses the gasket around the hole.

Captive neck. The 6.00 mm plain neck is below the thread major diameter, and it is the zone a retaining ring or a panel escutcheon grips. That is what makes the screw captive: it turns and travels, but it stays with the panel when the cover is opened.

Two drives. The straight knurl is the hand drive; a 1.60 mm slot across the full face is there for a blade when the panel is stiff or the screw has been in place for a while. Both work on the same part and neither interferes with the other.

Together these decide the assembly: the knob turns by hand, the cone centres and seals, the neck keeps the screw on the panel, and the nickel finish keeps the knob bright in a visible location.

Knob, Cone and Neck

The body is carbon steel wire, with grade and heat number on the batch record; stainless is available on request for the same form. The knob is upset on a multi-station header and the straight knurl is formed in the die rather than cut, so the flutes are continuous and the crown edge stays clean.

The slot is cut after the knurl and before plating. Cutting it after knurling keeps the slot concentric with the shank, and cutting it before plating means the slot is plated with the rest of the part, which is what keeps the nickel from accumulating only at the edges.

The cone seat is formed in the heading die under the knob. Its angle and seat diameter have to match the countersink in the panel; a cone that is too steep sits on a narrow ring and marks the panel, and one that is too shallow bottoms in the countersink and leaves a gap at the panel face. Both are checked on the first article against the customer’s panel.

The neck is left plain and turned below the thread major diameter. Its length of 6.00 mm is the captive zone, and it is the dimension a retaining ring or an escutcheon is designed around. Turning it below the major diameter is what allows a clip or a plate to pass over it and then stop at the thread.

The thread is rolled from the neck to the blunt point. On a knurled head locking screw the thread is deliberately short relative to the knob: the screw has to travel through the captive zone before it engages, and the engaged length is what the drawing quotes. On a knurled head locking screw that travel is quoted as a range, not only as a thread length.

The Recorded Dimensions and What They Control

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. The recorded configuration on this page is a specific M5 part, and its numbers show how the dimensions fit together.

The numbers are worth reading together because they explain the part. A 16 mm knob on an M5 thread is a hand-drive ratio of about three to one: enough leverage to compress a gasket, not enough to strip a thread by hand. A 6 mm neck and a 13 mm thread mean the screw travels 19 mm in total, so the panel it is captive in has to allow that travel.

Slot width follows the knob, not the thread. A 1.60 mm slot is a standard blade width, and it is cut across the full face so the blade can be used at any orientation without hunting for a groove. On a plated part the slot is checked after plating, because the same 3 to 8 µm that keeps the knob bright also narrows the slot. Every batch of knurled head locking screws is checked on both, in the plated condition.

Captive, Coned and Two-Way Drive

A knurled head locking screw is specified where a cover or a panel is opened in service and the fastener must not be lost. The features that make that work also set the limits of the part.

Captivity is the point of the part and the part most often left out of a specification. The neck alone does not make a screw captive; it gives the retainer somewhere to sit. Where the panel has no retainer, the screw is simply a thumbscrew with a step, and the drawing should say so rather than implying a function the assembly cannot deliver. That distinction is what separates a captive knurled head locking screw from a plain thumbscrew.

The cone is what makes the part seal as well as centre. On an access cover the panel sits in a countersink, and the cone pulls it down evenly so the gasket around the hole is compressed in a ring rather than at one point. That is why the cone angle is a quoted dimension and not a die detail: an 82-degree cone in a 90-degree countersink touches on a line and leaks.

The two drives cover two different situations. The knurl is what the operator uses every day, with the screw finger-tight; the slot is what a technician uses when the cover has been closed for a long time or the gasket has taken a set and the screw needs a little more than fingers can give. Both are part of the knurled head locking screw design rather than an afterthought.

Eco Nickel and Its Thickness

The recorded finish is eco nickel at 3 to 8 µm per surface. Nickel gives a bright, hard surface that holds up on a knob that is handled daily, and it is the usual finish for a visible captive screw on an enclosure.

Finish Options for Captive Thumb Screws

Plating thickness matters on this part in two places: the thread and the slot. The thread is rolled before plating and gauged after, because 3 to 8 µm on each flank is enough to change a GO gauge from passing to tight. The slot narrows by the same amount on both walls, so a 1.60 mm slot is checked with the blade and not only with a gauge.

Nickel on a knurled knob also changes how it feels. A heavy deposit rounds the flute crests and makes the knob slippery in a gloved hand, which on a hand-drive part is a real loss of function. That is why the range is 3 to 8 µm rather than a single figure: the low end keeps the knurl sharp, the high end gives the brightness.

Where Knurled Head Locking Screws Are Used

Three assemblies where a captive knob is the point of the design:

Why Shi Shi Tong for Knurled Head Locking Screws

Four reasons that matter on a captive screw, each tied to what the drawing has to prove:

How These Screws Are Manufactured

Shi Shi Tong forms these knurled head locking screws on a multi-station header: the knob and the straight knurl are formed in the die, the cone seat is shaped under the knob, the slot is cut across the face, and the machine thread is rolled above the plain neck. The parts are eco nickel plated and sorted. The first part of every run is measured on the knob, the neck and the thread, and fitted in a panel sample, before the batch continues.

The sequence is what keeps the part true. The knurl is formed first because it moves material, the slot is cut afterwards because it has to be concentric with the shank, and the thread is rolled before plating because plating is part of the final dimension. Changing that order produces a knob that is off centre or a thread that will not gauge after the nickel goes on.

Inspection: Knob, Cone, Neck and Slot

What decides whether a knurled head locking screw passes is the knob, the cone, the neck, the slot, the thread and the plating. The inspection agreement covers those, and the criteria come from the drawing.

Knob and cone on the projector	Thread gauged after plating
Hardness testing against the property class	Salt-spray testing of the nickel plate

The cone is checked by fitting the part in a panel sample with its countersink. Measuring the angle on the projector proves the cone is the angle on the drawing; only the fit proves it seats on a face rather than on a line, and on a gasketed cover that difference is the leak.

The neck is measured for diameter and length, and it is also checked that no thread has crept into it. A rolled thread that runs into the captive zone stops the retainer from passing over, and the screw cannot be fitted at all, which is a failure that shows only at assembly.

Certificates and Material Documentation

Every shipment of knurled head locking screws is traceable to the wire it was made from. The grade and heat number are recorded on the material certificate supplied with the parts, together with the plating thickness record, 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, the inspection record for the criteria on the drawing and, where it is listed, the third-party report for the material or the plating. The documents carry the drawing revision and the batch number, so the paperwork can be matched to the parts.

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 captive screw the first article is fitted in the panel with its retainer, because the neck and the cone only prove themselves in the assembly. Buyers visit during the process to review samples and to see how the knurls are formed.

Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the header 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

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Knurled Head Locking Screw FAQ

Order Knurled Head Locking Screws

How a knurled head locking screw 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.