Die nomenclature

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D = outside diameter
(tolerance zone f8)

E = thickness

a = width of tooth

c = width of notch

b = diameter of hole for
fixing screw

α = rake angle

β = chamfer angle

γ = spiral angle

Cutting die tolerancce classes
For metric ISO threads, tolerance class 6g (≤ M 1.4 Tol. 6h) applies, for Whitworth pipe threads tolerance class A and for Unified National threads tolerance class 2A is the standard tolerance class.
6e for tolerance class "medium" is used, for example, when the bolt is subsequently provided with a thick galvanic protective coating. Dies 6e cut approx. 0.03 mm smaller than 6g.

Chamfer
The standard chamfer length is 1.75 x pitch for HSS dies, 2 x pitch for HSS-E dies and 2.25 x pitch for LL dies.
For threads that are to be cut close to a shoulder, a chamfer length of 1.25 x pitch (70° short gate) is used.
A short chamfer cannot be achieved by face grinding, as the necessary gate diameter is then too small and the die no longer cuts correctly.

Preperation of workpiece
The workpiece to be cut is provided with a centric chamfer. This makes it easy to cut and obtains centric threads. The bolt diameter must be undersized compared to the nominal diameter of the thread to be cut (see reference value tables in our catalog page 120 to 123), cold welding in the die thread outer diameter and tearing out of the threads can thus be avoided. If the thread run-out on the bolt is provided with a recess, this prevents the die from breaking out during the return run.