Wire Insert Thread Class 3B 2

[Rich77]

Hello,

I need to produce a threaded hole for a wire insert. The drawing states " THREAD TO SUIT 0.138-32UNC-3B INSERT"

I have had conflicting advise from different tool suppliers for tap selection. One supplier has said that the tap I require is 2B class and the 3B tolerance is achieved by the wire insert selection. The other says the threaded hole requires a 3B class tap.

Does anyone have any experience with this?

Looking forward to your response.

Rich.

 

[btrueblood]

According to the Helicoil website, the tolerance class of the inside thread form depends on the threaded hole tolerance, i.e. you buy different taps if you want 2B or 3B class internal threads.

https://www.stanleyengineeredfastening.com/tools-and-systems/accessories/heli-coil-taps-and-gages

 

[Screwman1]

You use the special Helicoil tap for this application prior to installing the insert. Helicoil makes oversized gages ($$$) to work with their taps if you need to gage the tapped hole prior to installing the insert. The whole system is designed to work together to give you a 3B thread after installation.

 

[Rich77]

Thanks for the quick response. Looks like I need to purchase a different Tap and Gauge. Useful link btrueblood