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
Hydraulic torque wrench hydraulic torque wrench is significantly quieter, lighter weight and more accurate than pneumatic impact wrenches capable of similar torque output, making it an appealing alternative for many users to the very loud and cumbersome impact wrenches or torque multipliers which were formerly the only viable option for working with very large nuts and bolts until the hydraulic torque wrench was introduced. The Hydraulic Torque wrench was invented in 1968 by George A. Sturdevant. Bolt tensioners are an alternative to hydraulic torque wrenches, but not as commonly used. The most dangerous part of a hydraulic torque wrench is the reaction member,