Tap size for helicoil insert?

[spiffywebcreations]

Does anyone know the tap size for a 7/16-20 helicoil insert? I bought a used kit on EBay and the tap in it is not the correct size.

I have the hole drilled out to 29/64, as called out in the directions.

I'm afraid it's not a normal thread size, and there for a special tap is required - at a cost i'm sure I won't like.

 

[muleman]

I would think it was a 1/2-20 with that tap drill size. 27/64 is nominal for 1/2-13.

 

[spiffywebcreations]

that's what I always thought too - it was basically the next thread size up...but the Helicoil website tells you every other detail BUT the thread size...

I know the tap part number is 7FPB, it's an STI tap, and the tap major dia is .5062

 

[3MT]

Helicoils require a special tap. You can't use a regular tap to install a helicoil.

 

[tommu56]

the helicoil tap is the same pitch as the original thread the major diamater is bigger to give room for the coil to fit in

I prefer jergens inserts my self
you can replace the inset by drilling out the lock keys and spinning them out threading in a new tap the locks in
we used a lot of them in aluminum .

http://www.jergensinc.com/site/product_detail.aspx?group_no=3017


tom