On technical drawings, the undercut is often indicated with a simplified callout:
“UNDERCUT ACC. TO UNI ISO 4755”
Or dimensioned explicitly:
“GOLA M6 – a max 2.0”
When to use the table:
| Standard | Region | Key Differences from UNI ISO 4755 | |----------|--------|------------------------------------| | DIN 76-1 | Germany | Slightly larger undercut widths for some diameters; includes trapezoidal threads. | | UNI 4749 (obsolete) | Italy | Had distinct values for fine vs. coarse; now replaced by ISO 4755. | | ANSI B18.3 | USA | Inch-based; uses a different undercut geometry for socket head cap screws. |
Important: When designing for global markets, prefer ISO 4755 unless a customer explicitly requests DIN 76-1. tabella gola uni iso 4755
If you are designing a part or checking a measurement:
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. On technical drawings, the undercut is often indicated
UNI ISO 4755 is the Italian adoption of the international standard ISO 4755. The full title is usually related to "Fasteners — Bolt and screw ends — Chamfers and ends."
When people look for a "tabella gola" (groove table) under this standard, they are typically looking for the specifications regarding the ** chamfer (smusso)** or the run-out (gola) at the end of the thread. “UNDERCUT ACC