The minimum size of a complete set of Allen wrenches is 3, and the corresponding relationships are S3 = M4, S4 = M5, S5 = M6, S6 = M8, S8 = M 10, S 10 = M 12, s12 = m/kloc-.
Calculation method of thread bottom hole diameter before tapping: for brittle materials, according to the basic size-1.0826 pitch, for plastic materials, according to the basic size-pitch +0. 1, brittle materials are in a pure cutting state when tapping, and the bottom hole size is the diameter of thread bottom circle. When tapping plastic materials, due to the plastic deformation after stress, the materials will move to the thread diameter direction, so the bottom hole should be appropriately enlarged.
For threaded holes below M6, regardless of material properties, the basic size-pitch is uniform.
Extended data:
The outer diameter of metric thread is in millimeters, such as 6, 8, 10, 12, 18, 20mm, and the pitch is also in millimeters, such as 0.5, 0.75, 1, 1.5, 2.
The outside diameter of English thread is in inches (each inch is equal to 25.4 mm), such as 3/ 16, 5/8, 1/4, 1/2, etc. Therefore, the outer diameter readings measured by metric calipers often have irregular decimals.
English pitch is expressed by the number of teeth per inch. Set the caliper to 25.4 mm and align a ruler tip with the thread tip. If the other ruler tip is aligned with the thread tip, it is an English thread. If the top of the thread is not aligned, it should be metric thread.
When measuring the pitch, it is best to print the tip of the thread on white chalk, which is clear and convenient for measurement. When measuring metric pitch, the length should be measured, such as 10, 15, 20 mm, etc. Count the number of teeth and calculate the pitch.