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Tabella Gola Uni Iso 4755 May 2026

Guida Definitiva alla Tabella Gola UNI ISO 4755: Dimensioni e Progettazione Nel mondo della progettazione meccanica, la gola di scarico

(thread undercut) è un dettaglio spesso sottovalutato ma fondamentale per garantire il corretto montaggio e la durata dei componenti filettati. La normativa di riferimento per le filettature esterne metriche ISO è la UNI ISO 4755 Cos'è la Gola di Scarico UNI ISO 4755?

La norma specifica la forma e le dimensioni delle gole di scarico per viti, bulloni e prodotti similari. La sua funzione principale è permettere a un componente accoppiato, come un tappo o una spalla rettificata, di andare a battuta perfettamente contro la faccia del pezzo, eliminando l'interferenza causata dal tratto di filetto incompleto. Tabella Dimensionale UNI ISO 4755 (Estratto) Le dimensioni della gola dipendono direttamente dal passo della filettatura (P) . Di seguito i valori principali espressi in millimetri: Diametro Gola ( Raggio (r)

: Diametro del fondo della gola (tolleranza h12 o h13 per diametri piccoli). : Corrisponde tipicamente a Angolo di transizione 30 raised to the composed with power Perché è fondamentale in officina? Montaggio a filo

: Senza la gola, la "fuga" del filetto impedisce al dado o alla flangia di toccare la spalla del bullone. Riduzione delle tensioni tabella gola uni iso 4755

: Una gola ben raccordata riduce l'effetto intaglio, migliorando la resistenza a fatica del componente. Lavorazione CNC

: Facilita l'uscita dell'utensile durante la tornitura o la rettifica. Differenza tra UNI ISO 4755 e DIN 76 ISO-4755-1983.pdf - iTeh Standards

2. Why the “Tabella Gola” is needed

Without a standardized undercut:

  • A threaded part cannot screw flush against a shoulder because the thread run-out leaves an incomplete thread profile.
  • Manufacturing (tapping, die-cutting, thread milling) would be less predictable.

The gola (undercut) provides a clearance groove with a controlled diameter and width, ensuring: Guida Definitiva alla Tabella Gola UNI ISO 4755:

  • Full seating of mating parts.
  • Reliable thread depth up to the end of the part.
  • Reduced stress concentration.

7. Limitations

  • The standard does not cover:
    • Threads other than ISO metric (e.g., UN, UNC, UNF, trapezoidal, pipe threads).
    • Very small threads below M1 (pitch < 0.2 mm).
  • For special applications (e.g., aerospace), customized undercuts are often specified.

Why Does the "Gola" Exist?

Without a standardized undercut (groove), two problems occur:

  1. Stress Concentration: A sharp corner between the head/shank and the thread acts as a stress riser, leading to fatigue failure.
  2. Interference: When threading into a hole with an internal thread (like a tapped blind hole), the incomplete thread at the start of the bolt might bottom out before the head clamps.

The gola solves both by providing a smooth, recessed relief.

4. Practical Application

If you are designing a part or checking a measurement:

  1. Check the Tip: Is it flat with a $45^\circ$ bevel? If yes, it meets ISO 4755.
  2. Check the Run-Out: If you are looking at where the thread stops near the head or shank, check ISO 4757 (often confused with 4755). The profile is usually defined by the tool withdrawal path.

4. Main Applications

  • Screw fastening up to a shoulder – using an undercut on the bolt shank near the head.
  • Internal thread undercuts – to allow taps to run out without leaving incomplete threads in blind holes.
  • Precision mechanical assemblies (automotive, aerospace, machine tools) where axial positioning is critical.

ISO 4755 vs. Other Undercut Standards

It is vital to distinguish UNI ISO 4755 from similar standards: A threaded part cannot screw flush against a

| Standard | Name | Key Difference | | :--- | :--- | :--- | | UNI ISO 4755 | Undercuts for metric threads (long version) | Standard undercut for general engineering. | | DIN 76-1 | Undercuts for metric threads | Almost identical to ISO 4755 (Germany uses DIN 76-1). In practice, they are interchangeable for most sizes. | | DIN 78 | Undercuts for bolts with reduced shank | Different geometry; used specifically for shoulder bolts. | | ISO 3506 | Mechanical properties for stainless steel | Refers back to ISO 4755 for undercut dimensions, but property classes (A2-70, A4-80) have different fatigue limits. |

Tip for buyers: If a supplier says "conforms to DIN 76-1," they also conform to UNI ISO 4755 for 95% of metric sizes. However, always verify the specific a dimension if you have a blind hole with a specific depth.

1. Introduction

In threaded fastening technology, the undercut (Italian: gola) is a critical yet often overlooked geometric feature located at the transition between the threaded shank and the unthreaded body of a screw or bolt. The standard UNI ISO 4755 provides a harmonized table (tabella) defining the exact dimensions of this undercut for metric ISO threads.

Understanding and applying this standard is essential to ensure that threads engage fully, stress concentrations are minimized, and assembly interference is avoided.