Hexagon fit bolts are fit bolts with a hexagon head whose shank is precisely toleranced and fits into a correspondingly machined bore without play. Unlike ordinary hexagon bolts, where the shank diameter is smaller than the clearance hole, the closely toleranced fitted shank fills the bore almost completely. As a result, the bolt not only clamps the components together but also fixes their position relative to one another with precision – while still offering a hexagon head that is easily accessible for assembly with a wrench.
While a standard bolt absorbs transverse forces predominantly through friction between the clamped surfaces, the hexagon fit bolt additionally transmits any transverse forces through a positive (form-fit) connection via its fitted shank. This makes it the preferred solution wherever components need to be positioned precisely relative to one another, secured against lateral displacement, and still fastened using a conventional hexagon drive.
The key feature of a hexagon fit bolt is the cylindrical, closely toleranced fitted shank between the hexagon head and the thread. This shank is ground or turned to a defined fit dimension and matched to the reamed mounting bore of the component. The ratio of shank diameter to bore diameter determines how free of play the connection is, and is critical to its function. At the same time, the hexagon head ensures secure torque transmission during tightening and good accessibility even in confined installation situations.
On insertion, the fitted shank fills the calibrated bore almost completely, clearly defining the position of the components. Whereas a normal hexagon bolt allows a certain amount of bore clearance and derives its holding effect solely from friction between the clamped surfaces, the hexagon fit bolt ensures reproducible, precisely defined alignment through the positive fit of the shank.
Under forces acting transversely to the bolt axis, the fitted shank absorbs the load directly through its cross-section and transmits it by shear. The result is significantly greater security against lateral displacement of the components, since the connection does not rely solely on the friction generated by preload.
Compared with conventional hexagon bolts, hexagon fit bolts offer several design advantages: they position components precisely and repeatably relative to one another, they absorb transverse forces through a positive fit, and they reliably secure the position of the connection even under fluctuating loads. At the same time, the hexagon head allows simple, high-torque assembly with standard tools. This makes them particularly suitable for close-tolerance, safety-relevant connections where precise alignment and good accessibility are essential.
Hexagon fit bolts are used primarily where components need to be positioned exactly relative to one another and secured against transverse forces, while a hexagon drive is still required. Typical examples include securing couplings and gears on shaft flanges, positional fixing of bearing blocks and housing parts, connections in jig and fixture construction and tool and die making, as well as close-tolerance bolted connections in mechanical engineering, plant engineering and gearbox construction.
Hexagon fit bolts are predominantly manufactured from high-strength quenched-and-tempered steels, with the strength class selected to match the specific application. Depending on the field of use, corrosion-resistant or surface-treated materials are also used. Design and dimensions are based on the relevant standards for fit bolts with a hexagon head, while shank tolerance, geometry and strength are matched to the design specifications from the respective customer drawing.
For a hexagon fit bolt to deliver its advantages, precise preparation of the bore is essential. Since a play-free fit of the shank is required, the mounting bore is typically reamed or fine-bored and matched exactly to the fit dimension of the shank. The bolt can then be tightened via the hexagon head to a defined torque, ensuring reproducible positional accuracy and preload.
While an ordinary hexagon bolt is designed for simple assembly with bore clearance and pure clamping, the hexagon fit bolt is deliberately designed for a play-free, closely toleranced shank fit. This higher manufacturing effort is not an end in itself but the actual function: it ensures a precisely positioned connection that is resistant to transverse forces under exactly the conditions where standard bolts reach their limits – while retaining the practical advantage of a hexagon drive.
We manufacture hexagon fit bolts as custom bolts precisely to your drawing – matched to the material, strength class, shank tolerance, head shape and geometry of your application. For further information, please see our product range of custom bolts to customer drawing.
Whenever components need to be positioned exactly and repeatably relative to one another, or when transverse forces need to be absorbed through a positive fit and displacement of the connection must be reliably ruled out – and when an easily accessible hexagon drive is also required for assembly.
Yes. Geometry, shank length, fit dimension, head shape, material and strength class can all be matched to your application. Simply send us your drawing or sample.
Do you need hexagon fit bolts to drawing? Send us your drawing (PDF, DXF, STEP) or your sample – we will check feasibility and prepare a quote for you. Please use the inquiry form at the bottom of this page.
Do you need hexagon fit bolts to customer drawing? Send us your drawing (PDF, DXF, STEP) or a sample – we will check feasibility and prepare a quotation. Please use the inquiry form at the bottom of this page.
Email: info@pattberg-mbt.de
Phone: +49 234 58 88 79-0
Certified quality: PATTBERG has been certified to DIN EN ISO 9001 since 2008, and additionally to DIN EN ISO 14001 since 2024.
