Square head held with a spanner
The broad square head bears flat on the part and can be held with a spanner while the hex or square nut is tightened.
Bolts & Fittings
Machine Bolt
Machine Bolt is a square-headed bolt with a hex or square nut, used where a broad head bears on the part and can be held with a spanner. In fencing it joins palisade rails to posts through the fish plates, and fixes post brackets and gate hardware. For palisade it comes as cup square and T-head bolts with shear nuts. Specify the diameter, length, finish and the quantity you need.
At a glance
Machine Bolt at a glance.
1/4 to 1/2 in diameter, 1-1/4 to 12 in lengths
1/4 to 1/2 in (M6 to M12), 1-1/4 to 12 in (32 to 300 mm) long, UNC or metric coarse thread, Grade 2 or Grade 5 (Class 4.6 or 8.8), hot dip galvanized. Cup square and T-head versions with shear nuts for palisade.
Structural attachment in post and rail assembly
Joins palisade rails to posts through the fish plates, and fixes hinges, brackets and rail clamps to posts.
Also known as
Spanish-speaking crews call it tornillo cabeza cuadrada.
- Español (US)
Hold the head while tightening the nut
Position the bolt through the component; hold the square head with a spanner so it cannot turn. Thread the nut onto the bolt end and tighten. The broad head provides bearing surface and load distribution, while the nut can be tightened without spinning the head out of position.
Choosing between
Carriage bolt or machine bolt.
Both bolt fencing steel assemblies. The head design determines where you can place the wrench and how securely the bolt locks in place.
Common applications
Where it is used.
Fish plate fastening in palisade rails
Join palisade rails to RSJ posts through the fish plates with M12 bolts and shear nuts.
Gate hinge and hardware mounting
Attach hinges, latches, and guides to gate posts with machine bolts held fast by the head, keeping hardware in precise position through repeated gate operation.
Post bracket and rail-clamp installation
Fasten brackets and rail clamps to posts in chain-link and farm-gate systems where the bolt head must sit flat and bear against the clamp or bracket surface.
Questions answered
Common questions.
What else is a machine bolt called?
In the US it's a square head machine bolt. Spanish speakers call it a tornillo cabeza cuadrada.
What machine bolts are used for palisade fencing?
For palisade fencing, GV supplies M12 cup square bolts that join rails to posts through fish plates and M8 T-head bolts that fix the pales. Both are Class 8.8 material, hot dip galvanized. Shear nuts snap off once tightened, preventing removal from outside.
In palisade and gate hardware
Machine Bolt joins the rails and posts of steel palisade fencing and fixes the brackets and hardware of chain-link and farm gates.
Explore fencing systems ↗Machine Bolt specifications
Machine Bolt configuration
ParameterUS / PrimaryMetric / Additional
Size1/4-1/2 inM6-M12
Length1-1/4-12 in32-300 mm
HeadSquare headSquare head; cup square and T-head bolts for palisade
NutsHex or square nutsHex nuts; shear nuts for palisade
GradeGrade 2, Grade 5Class 4.6, 8.8
FinishHot Dip GalvanisedHot Dip Galvanised
Fencing Systems
Related components
Palisade Fence
Palisade Fence
Pale profile: D section or W section; triple pointed, single point, round top, notched round top or flat top · Pale thickness: 2.0, 2.5, 3.0 mm; up to 4.0 mm
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