Hobson Cup Head Bolt & Nut, M6 / 20mm

The Hobson cup head bolt & nut is a domed-head bolt supplied with its nut, in grade 4.6 mild steel with a galvanised finish. A cup head bolt has a smooth domed head with no drive, so it is tightened from the nut end. Cup head bolts are normally made with a square section under the head that holds the bolt in place while the nut turns.

Class 4.6 is low tensile carbon steel, and corresponds to imperial grade 2. The steel is cold mild steel for some items and hot mild steel for others. The Steel line on each item shows which. Pack quantity changes with size and length and is shown for each item.

Where this product is used

• Fencing, gates and timber framing, where the square neck locks into the timber so the bolt does not spin as the nut is tightened
• Pergolas, carports and timber frames where the rounded head faces out and no spanner is needed on the head side
• Trailer sides, farm gates and rail fences where a smooth head will not snag
• General-purpose light fabrication, framing and non-critical joints
• The 105 items cover diameters from M6 to M20 and lengths from 20mm to 400mm, confirm the size against your drawing before ordering

Features

• 105 items: M6 x 20mm to M20 x 350mm
• Domed cup head, supplied with nut
• Grade 4.6
• Galvanised finish
• Pack quantity shown for each item
• General-purpose mild steel, class 4.6

Key specifications

Choosing the right option

Choose the thread size first, then the length: the bolt has to pass through all the parts, any washer and the nut.

Treat the finish as outdoor-capable zinc, and check the item description for hot dip when that matters to the job. Close to the sea, within about 1 km, 316 stainless is generally the better choice.

Class 4.6 is the general-purpose mild steel class, used where a joint does not need a high tensile fastener. For load-critical, structural or lifting joints, confirm the fastener against the engineer's specification. Fasteners are not lifting rated unless marked.

Related cup head bolts: Hobson Metric Cup Head Bolt & Nut, Grade 4.6, Mild Steel, Zinc, M6 to M12, Hobson Cup Head Bolt & Nut, Class 4.6 UTS, Hot Dip Galvanised, M6 to M24, Long Lengths and Hobson Cup Head Bolt & Nut, Class 8.8, Hot Dip Galvanised, M6 to M24.