Can anyone tell me the correct size mandrel for rivet nut setter?

[Just a Jeep]

I am replacing my fender flares and I need to replace the nutserts in the fenders. I bought a rivet nut setter kit but none of the mandrel fit. One was close but the threading seemed to course. Can anyone tell me the correct size mandrel or what kit to by that will have the correct one?
Thanks !!

 

[NOTNSUV]

I'd expect it to be 1/4-20. Can't say for sure.
Could also be M6 or M8 stuff.

 

[Viking Jeeper]

You can use whatever size works for you but my flares on my 06 were M5

 

[mrblaine]

You can use whatever size works for you but my flares on my 06 were M5

Yes they are as are all the flare nutserts.

 

[Just a Jeep]

Yes they are as are all the flare nutserts.

Thanks, now it’s off to Amazon!!