Tap Size oddity??

[T_Dubs]

Not really anything important, but I'm curious now. Going through my drawer of random drills and taps, I came across an 8-32 tap. Picked it up with a 10-32 and the no8 was noticeably bigger. I thought, weird, let me check. 10-32 taps measure around .194 across the cutting flutes with just a quick caliper check. 8-32 measures .206.

WTH?? Like I said, it doesn't matter as I don't need it, just piqued my curiosity. Only writing on the tap is OSG NO8-32NC GH3 STI, HSS 6230. Couldn't come up with anything online for a matching product.

What am I missing here?

 

[Booze Daily]

STI tap?

 

[T_Dubs]

disregard, totally missed that. Thanks!!

 

[Herding Cats]

I didn't look anything up but my guess is the TI is short for STI. Meaning it's a helicoil tap.

 

[T_Dubs]

It is STI, I mis-typed. I never use STI taps so it didn't even cross my mind. Should probably delete the thread lol

 

[Herding Cats]

Should probably delete the thread lol

It contains some valuable info that could help someone in the future. There was a time not all that long ago I did not know what STI stood for (screw thread insert). One could spend many years in the industry and never see one so I think it's a pretty good topic.

Most every machinist is going to know what a helicoil is but not all will know what a tap labeled STI is

 

[Vancbiker]

I’ve seen plenty of instances where a new machine operator grabbed an STI tap and promptly crunched it into a normal tap drill sized hole. Even a few times where on investigation of the incident, the operator did not question why they the new tap they grabbed needed a larger collet .