The formula for calculating the inner diameter of the thread tap:
1.Formula: tooth outer diameter-1/2 × tooth pitch
Example 1: Formula: M3×0.5=3-(1/2×0.5)=2.75mm
M6×1.0=6－(1/2×1.0)=5.5mm
Example 2: Formula: M3×0.5=3-(0.5÷2)=2.75mm
M6×1.0=6－(1.0÷2)=5.5mm
2. Conversion formula for general inch wire tapping:
1 inch = 25.4mm (code)
Example 1: (1/4-30)
1/4×25.4＝6.35 (tooth diameter)
25.4÷30=0.846 (tooth pitch);
Then 1/4-30 converted to metric teeth should be: M6.35×0.846
Example 2: (3/16-32)
3/16×25.4＝4.76 (tooth diameter)
25.4÷32=0.79 (tooth pitch)
Then 3/16-32 converted into metric teeth should be: M4.76×0.79
