The degree of cold welding in ultra-high vacuum (10−9torr) was determined for 45 metal combinations. Static coefficients of friction were measured after stationary contact under 9.2-lb load for 300 hours at 200 C. Kinetic coefficients were measured at a velocity of 0.4 inch/second immediately after breakaway. Nearly all of the metal combinations tested exhibited maximum kinetic coefficients higher than the corresponding static coefficients. Metal transfer was from rider to ring when the rider was softer but followed no pattern when the ring was softer. Very little correlation was found between the friction characteristics of the metals and their physical properties.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis. Minnesota, October 18–20, 1966.