Knurled Head Thumb Screws With Shoulder

We make knurled thumb screws with a shoulder in blue zinc plated carbon steel: a straight-knurled head, a single slot, a plain shoulder and a half thread, quoted from M1 to M14. Knurl, slot, shoulder tolerance and thread come from your drawing, and the first article is adjusted by hand and with a blade.

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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 These Thumb Screws Are

These knurled thumb screws are shoulder screws with a straight-knurled head, a single slot and a half thread, made in blue zinc plated carbon steel and quoted from M1 to M14 with Number 19. The knurl is the hand drive, the slot is the tool drive, and the shoulder under the head locates the joint.

Knurled head. A cylindrical head with a straight knurl around it, giving fingers something to grip.

Single slot. A straight cut across the top, so a screwdriver can take the torque the hand cannot.

Shoulder. A plain section that runs in a bore and carries the radial load.

Blue zinc. A bright zinc deposit with a blue-white chromate, the economical indoor finish.

Knurled thumb screws with a shoulder are used where something has to be adjusted by hand and then stay where it was put: stops, clamps and covers on instruments and machines, where a tool would slow the job down and a plain head would not hold.

Two Drives in One Head

A knurled thumb screw with a slot gives two ways to turn it, and the two are used for different things. The knurl is for adjustment: an operator turns the screw by hand, with the grip the knurl gives, and stops when it feels right. The slot is for the occasional torque the hand cannot reach, usually when the joint has to be firm rather than merely closed.

Having both does not come free. The slot is cut across the top of a knurled cylinder, so it takes away the crest of the knurl where the blade passes and leaves thin sections at the rim; a blade used hard can chip the crests beside the slot, and the head then has a smooth patch exactly where the thumb would go. The slot is worth having, but it is the tool of last resort rather than the normal drive.

On knurled thumb screws the shape of the head makes the same point. A knurled head is tall enough to grip, which means it stands above the surface more than a pan or button head would; on a thumb screw that is accepted because the head is meant to be reached, but it rules the part out of any joint with a tight clearance above it.

The shoulder is the functional part under all of that. It runs in a bore, carries the radial load and sets the position the screw is adjusted to, and its fit is what decides whether the joint is firm when the thumb lets go. On a thumb screw the shoulder is often what the customer actually cares about: the knurl is how you set it, the shoulder is what stays set.

Blue zinc is the finish that goes with the economics. It is bright, thin and sacrificial, it keeps the knurl crisp and the slot sharp, and it suits an indoor part that is handled rather than washed.

Sizes, Slot and Shoulder

The recorded range is M1 to M14, with shoulder diameters and lengths made to the drawing. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. For knurled thumb screws the quotation carries head diameter and height, knurl pitch and depth, slot width and depth, shoulder diameter and length, and the thread.

Slot width is a fit against the blade, and slot depth has to leave enough head above the shoulder to keep the head rigid. On a knurled head both are constrained by the knurl: the slot interrupts the crests, and the deeper it goes the more of the grip it removes.

Shoulder length is quoted separately from overall length. On a thumb screw the shoulder is often the adjustment setting, so it is the number the customer’s joint depends on rather than a dimension that follows from the head.

Hand, Tool and Bearing

Three features define the part: the knurl, the slot and the shoulder. The first is the everyday drive, the second is the backup, and the third is what holds the setting.

The knurl is the reason the part exists. Anywhere an operator has to adjust something by hand without hunting for a tool, a knurled head is the simplest answer, and the shoulder underneath makes the adjustment repeatable.

The slot is the reason it is practical. A joint that needs to be firm once in a while cannot be held by fingers alone, and one slot gives the occasional firmness without adding a second head form to the kit.

Blue Zinc on a Knurled Head

The recorded finish is blue zinc plating over carbon steel. It is a thin, bright, sacrificial deposit; thin enough that the knurl keeps its shape and the slot keeps its width, bright enough to look finished, and sacrificial so that a scratch on a crest protects the steel around it.

Finish Options for Knurled Thumb Screws

On knurled thumb screws that are adjusted often, a thin coating is the right one: anything thicker rounds the crests and the knurl stops biting, which is the failure that makes a thumb screw unusable rather than merely worn.

Where the joint is wet, the material should change rather than the coating. A knurled head in damp service corrodes at the crests first, because they are the thinnest points and the ones that get handled.

Where These Screws Are Used

Three assemblies where knurled thumb screws with a shoulder are the fixing:

Why Shi Shi Tong for Knurled Thumb Screws

Four reasons that matter on a hand-driven part, each tied to what the drawing has to prove:

How These Screws Are Manufactured

Shi Shi Tong forms the head and shoulder of these knurled thumb screws, cuts the straight knurl, machines the slot, rolls the half thread and blue zinc plates the parts. The first part of every run is measured on head diameter, knurl pitch and depth, slot width and depth, shoulder diameter and length before the batch continues.

Cutting the slot after the knurl is the step that decides how the head looks and holds. The cutter has to stop before it takes too much of the crest, and the two edges where the slot meets the knurl are where a blade will chip the head later; a slot cut too deep leaves thin crests that break away the first time a screwdriver is used.

Inspection: Knurl, Slot, Shoulder

What decides whether knurled thumb screws pass is the knurl, the slot, the shoulder and the thread. The inspection agreement covers those, and the criteria come from the drawing.

Knurl and slot on the projector	Thread gauged after plating
Hardness checked on the wire	Coating proved by salt spray

The knurl is checked for pitch, depth and crest condition, the slot for width, depth and the radius at each end, and the shoulder for diameter and length. The thread is gauged after plating, and the coating is checked inside the slot.

The first article is turned by hand and then with the customer’s blade. A head that grips well but chips when the blade is used is still a part that fails in service, and only that sequence shows it.

Certificates and Material Documentation

Every shipment of knurled thumb screws is traceable to the wire it was made from and to the plating 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, the inspection record for the criteria on the drawing and, where it is listed, the third-party report for the coating. The documents carry the drawing revision and the batch number, so a repeat order keeps the same knurl and shoulder tolerance.

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 knurled thumb screws the first article is adjusted by hand and then with a blade, because grip and torque are both part of the function. 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 knurling and plating lines 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 Thumb Screw with Shoulder FAQ

Order Knurled Thumb Screws

How a knurled thumb 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.