Tabella Gola Uni Iso 4755 -

If you are a machinist turning bolts on a lathe, the "gola" is programmed into the threading cycle. Before the chasing tool cuts the thread, a grooving tool creates the undercut to the dimensions above. Using the wrong width (a) will cause the threading tool to crash or leave a sharp step.

Many engineers search for ISO 4755 expecting a table of dimensions. However, ISO 4755 is a "design rules" standard, not a dimension table itself. It dictates how the groove should be designed to ensure the screw functions correctly.

The standard specifically covers:

The "Gola" in this context usually refers to the V-notch or cutting flute found at the tip of the screw.

The tabella (table) in UNI ISO 4755 is organized by thread diameter (d) and pitch (p) . Below is a representative excerpt for coarse thread series (the full table extends up to M39 and includes fine threads).

| Thread Size (d x p) | Undercut Diameter (d₁) max | Undercut Width (a) max | Undercut Radius (r) ≈ | |---------------------|----------------------------|------------------------|------------------------| | M3 x 0.5 | 2.3 mm | 1.3 mm | 0.3 mm | | M4 x 0.7 | 3.0 mm | 1.6 mm | 0.4 mm | | M5 x 0.8 | 3.8 mm | 1.8 mm | 0.5 mm | | M6 x 1.0 | 4.6 mm | 2.0 mm | 0.6 mm | | M8 x 1.25 | 6.2 mm | 2.5 mm | 0.8 mm | | M10 x 1.5 | 7.8 mm | 3.0 mm | 1.0 mm | | M12 x 1.75 | 9.5 mm | 3.5 mm | 1.2 mm | | M16 x 2.0 | 13.0 mm | 4.0 mm | 1.5 mm | | M20 x 2.5 | 16.5 mm | 5.0 mm | 2.0 mm |

Notes:

Connecting rod bolts and cylinder head bolts almost always conform to an undercut standard (often derived from ISO 4755). When rebuilding an engine, mechanics look for this groove to confirm they are using OEM-grade fasteners, not cheap hardware store substitutes.

While ISO 4755 gives the design formula, actual dimensions are often found in the ISO 1478 (Tapping screw threads) or specific product standards (like DIN 7513).

However, for a standard Type F (Thread Cutting) screw, the groove geometry is typically defined by the thread diameter ($d$). The standard specifies the length of the incomplete thread and the shape of the point.

Typical Parameter Structure for a Tapping Screw Point:

| Thread Size (d) | Nominal Diameter (mm) | Approx. Point Length ($l_p$) | Groove/Flute Characteristics | | :--- | :--- | :--- | :--- | | ST 2.2 | 2.2 | Min 2.0 | Narrow cutting flute, sharp tip. | | ST 2.9 | 2.9 | Min 2.5 | Flute width approx. 20-25% of diameter. | | ST 3.5 | 3.5 | Min 3.0 | Increased cutting depth. | | ST 4.2 | 4.2 | Min 3.5 | Standard V-shape cutting geometry. | | ST 4.8 | 4.8 | Min 4.0 | | | ST 5.5 | 5.5 | Min 4.5 | | | ST 6.3 | 6.3 | Min 5.0 | |

Note: $l_p$ (Point Length) is often roughly 2 to 3 times the pitch of the thread.

Reality: Intuitively, removing material seems weakening. However, by eliminating a sharp corner, the groove increases fatigue resistance. A bolt with an ISO 4755 undercut will last longer under dynamic loads (vibration, rotating bending) than a bolt with a sharp 90-degree transition.

The complete UNI ISO 4755:2005 (including the full tabella gola with all diameters from M1 to M100+) is available for purchase from:

⚠️ This report is for informational purposes only. For manufacturing, always refer to the official standard document.

If you need the exact numeric table for a specific thread size (e.g., M6, M10, M16), let me know and I can extract the corresponding gola dimensions according to UNI ISO 4755.

La tabella GOLA secondo la norma UNI ISO 4755! Ecco una guida utile per comprendere e utilizzare questa tabella.

Cos'è la tabella GOLA?

La tabella GOLA è una tabella di tolleranze per le dimensioni di fori e alberi (o assi) secondo la norma UNI ISO 4755. Questa norma internazionale fornisce un sistema di tolleranze per le dimensioni di pezzi meccanici, al fine di garantire l'intercambiabilità e la corretta funzionalità dei componenti.

Come si legge la tabella GOLA?

La tabella GOLA è composta da diverse colonne che indicano: tabella gola uni iso 4755

I valori di tolleranza sono espressi in micron (μm) o in millimetri (mm).

Come si utilizza la tabella GOLA?

Per utilizzare la tabella GOLA, segui questi passaggi:

Esempio

Supponiamo di avere un foro con dimensione nominale di 50 mm e di voler applicare una tolleranza di H7. Consultando la tabella GOLA, possiamo leggere:

| DN | Tolleranza foro | Tolleranza albero | Gola | | --- | --- | --- | --- | | 50 | +0,000 / +0,025 | -0,050 / -0,025 | 0,025 |

In questo caso, il foro può avere una dimensione compresa tra 50,000 mm e 50,025 mm, mentre l'albero può avere una dimensione compresa tra 49,950 mm e 49,975 mm.

Conclusione

La tabella GOLA secondo la norma UNI ISO 4755 è uno strumento utile per determinare le tolleranze per le dimensioni di fori e alberi. Seguendo i passaggi descritti sopra, puoi utilizzare la tabella per garantire l'intercambiabilità e la corretta funzionalità dei componenti meccanici.

In the cold, sterile light of the Quality Control lab, Marco stared at the blueprint until the lines blurred. The part on his desk—a high-tensile steel drive shaft—was failing every stress test. It was a masterpiece of machining, except for one fatal flaw: the threads met the shoulder at a sharp, jagged angle. "Stress concentration," he muttered, rubbing his eyes.

He pulled a worn, oil-stained manual from his shelf and flipped to the section marked UNI ISO 4755.

"The Tabella Gola," his mentor, Old Man Moretti, used to call it. To the uninitiated, it was just a table of dimensions for "Thread Undercuts for ISO Metric External Threads." But to a machinist, it was the secret to survival.

The table didn't just provide numbers; it provided the geometry of relief. It dictated the exact width and depth of the groove—the gola—that must be carved into the metal where the thread ended. This tiny, vanished ring of steel was what allowed the nut to sit perfectly flush and, more importantly, ensured the shaft wouldn't snap under pressure.

Marco recalibrated the lathe. He followed the coordinates for a 1.5mm pitch: a depth of 0.5mm, a radius of 0.6mm. As the carbide tip bit into the steel, a perfect, smooth radius formed—a "Type A" undercut, exactly as the ISO standard demanded.

He ran the new part through the hydraulic press. The needle climbed, past the previous breaking point, into the green. The shaft held. By respecting the "Gola," Marco hadn't just followed a rule; he had turned a point of failure into a point of strength.

Standardization, he realized, wasn't about being rigid—it was about making sure the smallest details could carry the heaviest loads.

The UNI ISO 4755 standard (equivalent to the international ISO 4755:1983) specifies the form and dimensions of thread undercuts (known in Italian as gola di scarico) for fasteners with external ISO metric threads. These features are typically used at the end of a threaded shaft to provide clearance for a cutting tool or to allow a mating component, like a plug, to sit flush against a shoulder. Key Technical Specifications

The standard provides a specific geometry for the undercut, including a minimum transition angle of 30∘30 raised to the composed with power . The dimensions are categorized by the thread pitch ( ), which dictates the undercut diameter ( ), length ( ), and radius ( Dimensions Table (Abridged)

Below are recommended dimensions for standard metric thread pitches according to ISO 4755: Thread Pitch ( Undercut Diameter ( Undercut Length ( Max Length ( 0.5 0.75 1.0 1.25 1.5 2.0 2.5 represents the nominal diameter of the thread. Usage Considerations

Design Purpose: Used where a full thread up to a shoulder is not possible or necessary. It ensures the mating part can be tightened without interference from the thread run-out.

Alternatives: If a specific product standard (e.g., for a particular type of bolt) defines different undercut requirements, those take precedence over ISO 4755. If you are a machinist turning bolts on

Verification: This standard was last reviewed and confirmed in 2023, meaning the 1983/1986 versions remain current in industrial practice. ISO-4755-1983.pdf - iTeh Standards

The Essential Guide to UNI ISO 4755: Mastering Thread Undercuts

In precision engineering, the smallest details often determine the success of a mechanical assembly. One such detail is the thread undercut (or gola di scarico), governed by the UNI ISO 4755 standard.

Whether you’re a machinist or a mechanical designer, understanding this "tabella gola" is critical for ensuring that bolts, screws, and plugs sit flush against their mating surfaces without interference. What is UNI ISO 4755?

The UNI ISO 4755 standard specifies the form and dimensions for thread undercuts on fasteners with external metric ISO threads. It provides a standardized "relief groove" at the end of a threaded section, allowing a cutting tool to exit cleanly and ensuring a flat seat for the mating component. Why are Undercuts Necessary?

Tool Clearance: They provide space for the thread-cutting tool to finish its pass without crashing into a shoulder.

Flush Fitting: Without an undercut, a small radius or incomplete thread often remains at the base of a shaft, preventing a nut or part from seating perfectly flat.

Stress Management: Properly designed undercuts can reduce stress concentrations at the transition point of a fastener. Key Dimensions in the UNI ISO 4755 Table

The standard provides specific dimensions (in mm) tied to the thread pitch (

). Key parameters found in technical tables like Fasteners.it include:

(Undercut Diameter): The reduced diameter of the groove, often calculated based on the nominal diameter ( ) minus a specific value (e.g., for certain pitches).

(Undercut Width): The axial length of the groove. A common rule of thumb is that the undercut should be roughly times the thread pitch (

Transition Angle: The standard typically recommends a minimum transition angle of 30∘30 raised to the composed with power Sample Dimension Data Thread Pitch ( Undercut Diameter ( Data extracted from standard UNI ISO 4755 tables. Best Practices for Designers

Check Your Pitch: Dimensions for undercuts are strictly dependent on the thread pitch, not just the diameter.

Consult the Product Standard: UNI ISO 4755 is the general recommendation, but specific product standards (like those for specialized plugs) may take precedence.

Manufacturing Method: Be aware that rolled threads may have different requirements compared to machined (cut) threads, as noted in related standards like UNI 5709. ISO-4755-1983.pdf - iTeh Standards

La norma UNI ISO 4755 (corrispondente alla norma internazionale ISO 4755:1983) definisce la forma e le dimensioni delle gole di scarico per viti, bulloni e altri elementi con filettatura esterna metrica ISO.

L'impiego di una gola di scarico è fondamentale per permettere il corretto accoppiamento tra un elemento filettato e una superficie di appoggio (spallamento), eliminando l'interferenza causata dal tratto di filetto incompleto tipico dei processi di lavorazione meccanica. Tabella Dimensionale UNI ISO 4755

Le dimensioni della gola sono strettamente legate al passo della filettatura (P). Di seguito i valori standard espressi in millimetri per le filettature metriche più comuni: Passo filettatura (P) Diametro gola ( Larghezza gola ( Larghezza gola ( 0,5 0,7 0,8 1,0 1,25 1,5 1,75 2,0 2,5 3,0 : Diametro nominale della filettatura. : Diametro del fondo della gola.

: Distanza minima tra l'ultimo filetto completo e la faccia di appoggio. : Lunghezza massima complessiva della gola (circa Caratteristiche Geometriche e Scopo

La conformità alla norma ISO 4755 garantisce l'intercambiabilità dei componenti a livello internazionale e migliora l'affidabilità meccanica. The "Gola" in this context usually refers to

Forma della Gola: Presenta un profilo studiato per ridurre la concentrazione di tensioni (stress concentration) alla base del filetto, diminuendo il rischio di rotture per fatica sotto carichi dinamici.

Angolo di Transizione: La norma prevede generalmente un angolo di transizione minimo di 30° per facilitare il passaggio tra il diametro della gola e la parte filettata.

Campo di Applicazione: Si applica a tutti i prodotti filettati esternamente dove sia necessaria una gola (es. tappi, viti corte), a meno che la specifica norma di prodotto non indichi diversamente.

Relazione con UNI 5709: La UNI ISO 4755 ha parzialmente sostituito la vecchia norma italiana UNI 5709, che rimane tuttavia in vigore per la definizione delle distanze di spallamento e dei filetti incompleti (run-out). Vantaggi del Progetto Standardizzato

Montaggio Facilitato: Assicura che l'elemento filettato arrivi a battuta perfetta contro la superficie di appoggio.

Produzione Ottimizzata: Fornisce quote precise per gli utensili da taglio e le operazioni di rullatura, riducendo gli errori di programmazione CNC.

Riduzione dei Costi: La standardizzazione mitiga i rischi di componenti non accoppiabili, fondamentale nel commercio globale. ISO-4755-1983.pdf - iTeh Standards

The UNI ISO 4755 standard (equivalent to ISO 4755:1983) specifies the required form and dimensions for thread undercuts (Italian: gole di scarico) on externally threaded fasteners like bolts and screws. These undercuts are used to provide clearance for a mating part (such as a plug or sealing element) to sit flush against a shoulder when the thread cannot be run all the way to the end. Key Specifications of ISO 4755

The standard provides a tabulated set of dimensions in millimeters, which are determined by the thread pitch ( ) and the nominal diameter ( ) of the fastener. Undercut Diameter (

): The diameter of the recessed portion, typically smaller than the thread's minor diameter to ensure clearance. Undercut Width (

): The axial length of the relief section. Standard relief is often between one and three full thread pitches.

Transition Angle: The standard specifies the shape and transition between the threaded portion and the undercut, generally requiring a minimum transition angle of 30∘30 raised to the composed with power where applicable. Radii (

): Specifies the corner radii to minimize stress concentrations in the fastener. Typical Dimensioning Table (Summary)

The official ISO 4755 table provides specific values for each pitch. Below is a general guide on how dimensions are typically derived: Reference Formula/Requirement Diameter ( )

Linked to thread minor diameter to ensure mating part clearance. Width ( ) (Standard) or Radius ( )

Sized to avoid sharp edges while maintaining structural integrity.

For detailed engineering drawings or manufacturing, you can find complete technical PDFs and tables through specialized fastener resources like Fasteners.eu or official ISO portal snippets. g., M10 or M12)?

The UNI ISO 4755 standard (equivalent to the international ISO 4755) specifies the required form and dimensions for thread undercuts on bolts, screws, and similar externally threaded products. These undercuts are used to provide clearance for tools during machining or to ensure a flush fit for mating components. Technical Specifications for Thread Undercuts

The standard provides specific dimensions based on the thread pitch (

). Below are the typical recommended dimensions in millimeters: Undercut Diameter ( Undercut Length ( 0.25 0.4 0.5 0.7 0.8 1.0 1.25 1.5 1.75 2.0 Table data based on standard ISO 4755 dimensions. Key Design Rules Undercut Length ( ): Generally calculated as approximately times the thread pitch ( Transition Angle: A minimum transition angle of 30∘30 raised to the composed with power is typically maintained for the undercut profile.

Application: These dimensions are recommended unless a specific product standard (like those for specialized shoulder screws) provides its own undercut requirements. ISO-4755-1983.pdf - iTeh Standards