TAP-PLUG CARBON STEEL 3/16-32 NATIONAL STANDARD Machine Screw and Fractional Plug Taps. Precision Cut Threads, Accurately Formed For Consistent, Exact Threading. Heat Treated And Tempered For File Hard Threads, And Longer, Useful Life. Designed For Hand Cutting Applications. For Use With Tap Wrenches To Cut Internal Threads. 75% Thread Engagement. Plug Style Is The Most Commonly Used Style Of Tap -3 To 5 Threads Chamfered.