View Full Version : Taps

02-21-2004, 03:17 AM
I was looking thru a box of taps and came across S.T.I. marked on several. What do these letters stand for? There were several Heli-Coil taps in the same box and some metric. Actually some metric taps had this S.T.I. marked on them also. Travers list S.T.I. taps and says they are a 52 degree, but no more info. Thanks

02-21-2004, 09:38 AM

S.T.I. stands for Screw Tread Insert.

Unless I'm mistaken (someone will let me know if I am, I'm sure http://bbs.homeshopmachinist.net//wink.gif), they are used for helical coil threaded inserts. They are slightly oversized to accommodate the inserts outer thread. Don't really understand why, unless it is to allow insert to be screwed into tapped hole easier, since they can't take lots of screwing torque on their own. They probably expand slightly when the actual screw or bolt is inserted. IMHO.

Obviously, they are available in SAE and metric. Don't know about the 52*.