ThePipingMart Blog Fasteners What is Head Bolt? Uses and Dimensions

What is Head Bolt? Uses and Dimensions

Head Bolt

Head bolts are an essential part of any engine and play a critical role in keeping engines running smoothly. But what are head bolts, and what is their purpose? Let’s take a closer look at these vital components and explore how they work.

What is Head Bolt?

Head bolts are fasteners that hold the cylinder head to the engine block in internal combustion engines. They can also be used to attach other parts of the block as well, such as the camshafts, timing chain covers, and oil pan. They come in many different sizes, shapes, and materials, depending on their specific application.

Head Bolt Uses

Head bolts have several important uses. First off, they create a strong bond between two metal components that would otherwise move independently from one another due to thermal expansion and contraction caused by temperature fluctuations inside the engine block. They also help maintain proper compression by seating the cylinder head firmly against the block while still allowing a small amount of motion to account for thermal expansion and contraction. Finally, head bolts provide an extra layer of protection against potential leaks from the cylinder head into the rest of the engine block.

Head Bolt Dimensions

Diameter (d) Pitch Length of threaded portion* (b) Head Depth (k) Across Flats (s)
M4 0.7mm 14mm 2.8mm 7mm
M5 0.8mm 16mm 3.5mm 8mm
M6 1.0mm 18mm 4mm 10mm
M7 1.0mm 20mm 4.8mm 11mm
M8 1.25mm 22mm 5.3mm 13mm
M10 1.5mm 26mm 6.4mm 17mm
M12 1.75mm 30mm 7.5mm 19mm
M14 2mm 14mm 8.8mm 22mm
M16 2mm 38mm 10mm 24mm
M18 2.5mm 42mm 11.5mm 27mm
M20 2.5mm 46mm 12.5mm 30mm
M22 2.5mm 50mm 14mm 32mm
M24 3.0mm 54mm 15mm 36mm
M27 3.0mm 54mm 15mm 41mm
M30 3.5mm 66mm 18.7mm 46mm
M33 3.5mm 72mm 21mm 50mm
M36 4mm 78mm 22.5mm 55mm
M39 4mm 84mm 25mm 60mm
M42 4.5mm 90mm 26mm 65mm
M45 4.5mm 96mm 28mm 70mm
M48 5mm 102mm 30mm 75mm


Head bolts play an essential role in helping your engine run smoothly and efficiently. Not only do they keep critical components firmly attached together, but they also act as a sealant against potential leaks from one part of your engine into another. If you’re ever unsure about replacing or checking your head bolts, it’s always best to consult an expert who can answer any questions you may have about these important components!

Related Post