#40 NMTB X 1/4″ End Mill Holder (3900-1718) ~ For milling machines with #40 standard taper spindles. ~ Accepts single end mills. ~ Hardened and precision ground. ~ Drawbar end is 5/8″-11. For milling machines with #40 standard taper spindles. Hardened and precision ground. Accepts single and double end mills. Drawbar end is 5/8″-11.