National fine thread for 1/4” is 28 tpi, where are you using 1/4-24 , it’s not a standard size.
Next size down from 1/4” is 12/24.

Hey Henry, what material are you working with, maybe try a little lube.
I wonder if the NF and NC inserting tools are the same?

seems the proper term for the tool is "helicoil prewinder"

They can be fussy.  It is easy to push to hard and skip a thread starting them.  Get good lighting, put your good glasses on, get them good and square, push lightly and turn.  For lack of a better description I have had to push sideways on the install tool towards the leading edge of the insert as it starts. 

Maybe run the tap again just in case you malformed anything with the last 4 inserts.

Last edited by Bentworker (10/12/2024 3:11 PM)

Take a screw/bolt in the final size. File the end so you remove 1/2 the bolt with a straight line across the end of the bolt. That make a prewinder to screw the insert in I like to use red loctite on the insert, then clean thoroughly with brake cleaner spray once installed. Don’t put the final fastener in until the loctite is cleaned out or dried.