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Bolt Threads, Screw Heads and Drive Styles

Fastener Variety Specifics

Fasteners come in various different drive styles, each offering its own benefit to a specific application. Additionally, the head and the thread of the bolt or screw also offer the same specifications depending upon application type. Below you can find information on the drive type, bolt threading and screw head types.

Fastener Drives Fastener Heads Fastener Threads
Fastener Names & Titles


Drives

There are several more drive styles available, these are the styles that you will currently find on our site. Coming soon: Spanner, HTC / One Way, Clutch, Tri-Wing & More!

phillips head

PHILLIPS

The most common drive style. Shaped like a cross.

SLOTTED

A straight line cut into the center of the head.

SQUARE

A square shape, resists stripping out.

SOCKET / ALLEN / HEX

Driven with an Allen Key, hex wrench or socket driver, socket caps are often used for decorative or automotive applications.

TORX® / STAR / 6 LOBE

Torx® drive, also known as star drive resists stripping out and provides a more decorative drive finish.

TORX® WITH PIN / TORX® TAMPER Proof / TAMPER PROOF SECURITY

Torx® with pin security drive can only be driven with security bits and are used to prevent tampering and theft.


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Heads

The most common fastener heads are listed for your convenience.

phillips pan head screw
PAN HEAD
oval head screw
OVAL HEAD
truss head screw
TRUSS HEAD

round head screw
ROUND HEAD

FLAT HEAD

thumb screw
KNURLED THUMB HEAD
pancake head screw
PANCAKE HEAD

hex washer head screw
HEX WASHER HEAD
hex head bolt
HEX HEAD

TRIM HEX HEAD
socket cap screw
SOCKET CAP

button head socket cap screw
BUTTON SOCKET CAP
flat head socket cap screw
FLAT SOCKET CAP

button flange head socket cap screw
BUTTON FLANGE SOCKET CAP

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Threads

coarse thread screw
COARSE THREAD - UNC

Coarse threads are those with larger pitch (fewer threads per axial distance) and larger thread form relative to screw diameter. Example: 5/16-18

fine thread screw
FINE THREAD - UNF

Fine threads are those with smaller pitch (more threads per axial distance) and a smaller thread form relative to screw diameter. Example: 5/16-24


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Dissecting Fastener Names and Titles

18-8 Stainless Steel Phillips Pan Head Sheet Metal Screw 1/4”-20 x 1”


Diameter

The diameter of a screw is the measurement of thickness of the threaded portion.


Thread Pitch

Thread pitch represents the number of threads per inch. A UNC Coarse 1/4-20 screw has a threaded shank that is 1/4” in diameter and has 20 threads per inch. A UNF Fine 1/4-28 screw has a threaded shank that is 1/4” in diameter and has 28 threads per inch. Coarse threaded screws have fewer threads per inch. Fine threaded screws have more threads per inch.

coarse thread UNC fine thread UNF

Length & Proper Measuring

It is important to measure the length of a screw correctly for it to fit your application. If a screw is measured from under the head to the bottom of the threads, the length you order may end up being too long for your project. These simple rules should help keep things straight!



Want to measure bolts and screw? Look below to see the useful products we offer that makes measuring bolts, screws, nuts and washers easy!

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