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Surface Treatments For Taps


A hard superficial case, approximately 68 HRC, on the surface of a finished tap produced by means of a cyanide salt bath.

Purpose to resist abrasion and increase wear resistance due to the higher surface hardness.

Application Effective in both abrasive and tough materials, cast iron, plastic, stainless steel and high tensile strength steels.

Note! Care must be used when selecting nitride surface treatment because the increase hardness has a tendency to make the tap easy to chip and damage: Nitride not recommended for fast spiral flute taps and taps smaller than machine screw #2.

Double Nitride

Very similar to Nitride surface treatment with the exception that the hard case produced is deeper and harder than standard Nitride.

Application Extremely abrasive materials, plastic and gray cast iron.


Produced on surface of a finished tap by means of a steam furnace or cyanide salt bath. Well know heat treatment by which an oxide layer (Fe3O4) is formed on the surface of the tap. This will improve the adherence of threading agent which leads to improved output of taps.

Categories of Oxide
Steam Oxide:
To counteract galling or loading lubricate tap surfaces. Best for low carbon, leaded steel, stainless and gummy material.

Nitride and Oxide: For stress relief and light coating. Copper alloys of medium machinability.

Nitride Plus Steam Oxide: To add wear life and reduce loading. High speed production tapping, poor lubrication. Steam Oxide Plus Nitride: To add wear life and provide self lubrication. Use in cast iron.

Heavy Nitride Plus Steam Oxide: To add wear life in hard and dense metals. For tapping hard steel alloys, titanium, exotic metals and hard copper alloys.

Black Oxide: Helps retain cutting fluid in the working portion of the tap. Improves Performance in stainless steel, steel forgings, tool and die steel, and hot and cold rolled steels.

Hard Chrome

A surface treatment in the form of a thin hard chromium layer deposit (.0001 approximately). Increases the taps surface hardness and help reduce torque required to drive the tap.

Purpose: Proven very advantages in non-ferrous materials, such as copper, brass and bronze.

PVD Process (TiN, and TiCN)

Used to resist abrasion and chip welding. Biggest potential is for ferrous materials below 40RC.

TiN Titanium Nitriding

In the PVD treatment a 2-4 micron layer is formed.The coating is a gold color with a hardness of about 2300 HV with good friction characteristics and coating adhesion for improved tool life. TiN coating remains resistant up to 600 degrees centigrade.

TiCN Titanium Carbonitriding

A similar PVD process as TiN coating. Friction characteristics are still better than TiN. The TiCN coating remains resistant up to 400 degrees centigrade. The coating is a grey-purple color.


A method of surface treatment which has a marked influence on diminishing the possibility of "cold welding" especially good for machining softer steels.


A surface treatment through which the sliding property of the tap is increased, especially for machining different nonferrous metals.