Jarvis STI Tap, 1/2"-13 NC HSS GH3, Plug, USA, New: This is a new Jarvis: STI; 1/2"-13 NC; 4 Flute; HSS GH3; Plug Tap. It is used to make threads for Helicoil type thread repair inserts. It is sold with the Kent’s Tools 30 Day Satisfaction Guarantee.