Use a cutting fluid in either case. 1/2" thread depth means that you go 1/2" deep after accounting for the tapered-off section of the tap. All taps have this - it's a few threads that are stunted to let the tap start cutting easier. On typical taps (called "Plug" style taps),...
Very recently, a Doppler detection of pulsed ultrasound has been used to map fluid flows in blood vessels within a body, as described in IEEE TRANSACTIONS ON SONICS AND ULTRASONIC, VOL. SU-17, No. 3, JULY 1970 entitled "Pulsed Ultrasonic Doppler Blood-Flow Sensing." ...