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
Machine Bolts are square head bolts in the UK; in other languages they are Vierkantschraube (German) and tornillo cabeza cuadrada (Spanish).
- UK & Ireland
- Deutsch
- Español
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 hold fencing steel together. The head decides which one suits the joint.
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 is a machine bolt called in different regions?
Machine Bolt is sold as a square head bolt in the UK, a Vierkantschraube in German-speaking markets and a tornillo cabeza cuadrada in Spanish-speaking markets. In the US it is a square head machine bolt.
Which machine bolts are used on palisade fencing?
Machine Bolt for palisade comes as M12 cup square bolts that join the rails to the posts through the fish plates, and M8 T-head bolts that fix the pales, both in Class 8.8 and hot dip galvanized. Shear nuts snap off once tightened, so the fixings cannot be undone 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 systemsMachine 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
Specifications
Fencing Components
Barbed Wire Arm
Size: 14 G x 1-5/8, 1-7/8, 2, 2-3/8, 2-1/2 in post / — · Type: 3-strand 45° arm, 3-strand vertical arm, 6-strand V arm
Specifications
Fencing Components
Tension Bar
Size: 3/16 x 5/8, 3/16 x 3/4, 1/4 x 3/4 in / 20 x 5, 25 x 5 mm · Length: For 3-12 ft fences; 2 in shorter than the fabric / 0.9-3.6 m; 50 mm shorter than the fabric
Specifications