Roll Spring (Pin) Holders are accurately drilled to hold tiny roll springs so perfect alignment is obtained. The 1/16″ Roll Spring (Pin) Holder is notched to clear M16/AR-15 rear sights. The 3.5MM is excellent for holding the pin that retains the breech block on Sig handguns. This fine set has sizes 1/16″ (notched), 5/64″, 3/32″, 1/8″, 3.5mm and each made from 5/16″ Hex High Carbon 5160 Steel that is Bainite heat treated for strength. Single groove in grip section and laser marked for quick identification. 100% Made in the USA.