Stigma (letter) Stigma (letter) Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also used as a numeral symbol for the number 6. In this unrelated function, it is a continuation of the old letter digamma (originally Ϝ, cursive form ), which had served as a numeral since antiquity and was conflated with the σ-τ ligature in the minuscule handwriting of the Middle Ages. The στ ligature (, ) was one of many ligature forms that came into widespread use as
Torque screwdriver to at least 27Nm, with speeds of up to 2000 RPM. Cordless torque screwdriver are powered by batteries, usually rechargeable batteries with voltages from 3.6 to 18 volts. Dedicated screwdrivers for domestic use tend to operate off 3.6 to 4.8 volts and have relatively low maximum torque; drill/drivers operate off higher voltages and can deliver higher maximum torque. Cordless torque screwdrivers are used for the same applications as cordless screwdrivers without torque control. The pneumatic torque screwdriver is widely used for assembly requiring higher levels of torque. These tools are commonly used in automotive, aerospace and marine manufacturing. Pneumatic tools