Size: 0.25" . For cutting internal threads Standard, pipe and metric sizes Produced to exacting specifications Tough, carbon tool steel for long life Resist rust and tarnish Cut cleaner, more accurate threads Four flutes for extra chip clearance Right-hand threaded taps in plug, taper and bottoming styles Drill size permanently marked on each tap For pipe fittings Ideal where extremely tight fit is required Tap size: 1/4-18NPT Use drill size: 7/16"