Fitted bolts are fastening elements with a precisely toleranced shank that is fitted into a correspondingly machined bore without clearance. Unlike ordinary bolts, where the shank diameter is smaller than the through-hole, the shank of a fitted bolt is manufactured to a close tolerance and 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 a standard bolt transmits transverse forces mainly through friction between the clamped surfaces, a fitted bolt additionally transmits transverse forces positively through its shank. This makes it the preferred solution wherever components need to be precisely positioned relative to one another and secured against lateral displacement.
The key feature of a fitted bolt is the cylindrical, closely toleranced fitted shank between the head and the thread. This shank is ground or turned to a defined fit dimension and matched to the reamed bore in the component. The ratio of shank diameter to bore diameter determines how free of play the connection is, and is critical to its function.
When inserted, the fitted shank fills the calibrated bore almost completely, thereby clearly defining the position of the components. While a standard bolt allows a certain amount of bore clearance and derives its holding effect solely from friction between the clamped surfaces, a fitted bolt ensures a 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 via shear. The result is significantly greater security against lateral displacement of the components, since the connection does not rely solely on the frictional grip of the preload.
Compared with conventional bolts, fitted bolts offer several design advantages: they position components precisely and repeatably relative to one another, they absorb transverse forces positively, and they reliably maintain the position of the connection even under fluctuating loads. This makes them particularly suitable for close-fitting, safety-relevant connections where precise alignment is essential.
Fitted bolts are used above all where components need to be precisely positioned relative to one another and secured against transverse forces. Typical examples include fastening couplings and gears to shaft flanges, positional fixing of bearing blocks and housing parts, connections in jig and fixture design and tool and die making, as well as close-fitting bolted connections in mechanical engineering and gearbox construction.
Fitted bolts are predominantly manufactured from high-strength quenched and tempered steels, with the strength class matched to the specific application. Depending on the field of use, corrosion-resistant or surface-treated materials are also employed. Geometry, shank tolerance and strength are based on the relevant standards as well as on the design specifications from the respective customer drawing.
For a fitted bolt to deliver its advantages, precise preparation of the bore is essential. Since a clearance-free fit of the shank is critical, the receiving bore is generally reamed or fine-bored and matched exactly to the fit dimension of the shank. This allows the fitted bolt to be installed reproducibly and ensures the required positional accuracy of the components is reliably achieved.
While a standard bolt is designed for straightforward assembly with bore clearance and pure clamping, the fitted bolt is deliberately designed for a clearance-free, closely toleranced shank fit. This greater manufacturing effort is not an end in itself but the actual purpose: it ensures a precisely positioned, transverse-force-resistant connection under exactly the conditions where standard bolts reach their limits.
We manufacture fitted bolts as custom bolts exactly to your drawing – matched to the material, strength class, shank tolerance and geometry of your application. Further information can be found in our product area Custom Bolts to Drawing.
Whenever components need to be positioned precisely and repeatably relative to one another, or when transverse forces need to be absorbed positively and displacement of the connection must be reliably ruled out.
Yes. Geometry, shank length, fit dimension, material and strength class can all be tailored to your application. Simply send us your drawing or your sample.
Do you need fitted bolts to drawing? Send us your drawing (PDF, DXF, STEP) or your sample – we will check feasibility and prepare a quotation for you. Please use the inquiry form at the bottom of this page.
Do you need fit bolts to customer drawing? Send us your drawing (PDF, DXF, STEP) or your sample – we will check feasibility and prepare a quotation for you. 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.
