The "International Standard" is the same, with modifications noted, as that now in general use in France.

INTERNATIONAL STANDARD THREADS

At the "Congress International pour L'Unification des Filetages," held in Zurich, October 24, 1898, the following resolutions were adopted:

The Congress has undertaken the task of unifying the threads of machine screws. It recommends to all those who wish to adopt the metric system of threads to make use of the proposed system. This system is the one which has been established by the "Society for the Encouragement of National Industries," with the following modification adopted by this Congress.

1. The clearance at the bottom of thread shall not exceed part of the hight of the original triangle. The shape of the bottom of the thread resulting from said clearance is left to the judgment of the manufacturers. However, the Congress recommends rounded profile for said bottom.

3. The table for Standard Diameters accepted is the one which has been proposed by the Swiss Committee of Action. (This table is given above.) It is to be noticed especially that 1.25 mm. pitch is adopted for 8 mm. diameter, and 1.75 mm. pitch for 12 mm. diameter. The pitches of sizes between standard diameters indicated in the table are to be the same as for the next smaller standard diameter.

The Acme standard thread is an adaptation of the most commonly used style of Worm Thread and is intended to take the place of the square thread.

It is a little shallower than the worm thread, but the same depth as the square thread and much stronger than the latter.

The various parts of the Acme standard thread are obtained as follows:

Width of Point of Tool for Screw Thread

=

No. of Threads per inch

THE Acme standard tap-thread is cut with the same width of tool as the screw-thread and the diameter at the root is the same for tap and Clearance at bottom of thread between screw and nut is obtained by boring the nut blank .020 oversize.

screw.

The outside diameter of the tap is made .020 larger than the screw to give clearance between top of screw-thread and bottom of nut. Width of Point of Tool for Tap-Thread

3707

=

.0052.

.3707

No. of Threads per Inch

Diameter of Screw + .020.

.0052

.040.)

2 X No. of Threads per Inch

+ .020.

TABLE OF ACME STANDARD 29° TAP-THREAD PARTS