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No! A 1/4-20 thread has a smaller minor diameter, so there is not enough
material. Definitely use a 1/4-28 heli-coil.
Fortunately these days, there are other manufacturers selling "thread
repair kits", so it will be less expensive than you fear
(just check Amazon).
You may need to drill the hole a bit deeper (with the drill meant for the
heli-coil) so that the tap can reach in far enough.
A side benefit is that the heli-coiled thread in pot metal will be
stronger than before.
Also, a 1/4-20 coarse-thread screw would come loose more easily than a
fine-thread one.
Doug
On Sun, Jan 15, 2023 at 10:54 AM john <jniolon@att.net> wrote:
> I have a mirror mount on my truck door that held a rear view mirror.
> Unfortunately the mirror decided it didn't want to stay with my truck.
> So, I'm looking for a replacement. The mount is drilled and tapped for
> 1/4"-28 threads and most of what I find is 1/4-20. I'm wondering if I can
> re-tap the metal over existing threads with a 1/4-20 thread and it will
> hold...or will I just make a mess of it and make it broke. The drill side
> for the
> two thread sizes are within a 64th or so of being the same and the mount
> is 7/16" or so wide so I have some meat to play with...
>
> suggestions?
>
>
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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><div>No!=C2=A0 A 1/4-20 thread =
has a smaller minor diameter, so there is not enough material.=C2=A0 Defini=
tely use a 1/4-28 heli-coil.</div><div>Fortunately these days, there are ot=
her manufacturers selling "thread repair kits", so it will be les=
s expensive than you fear</div><div>(just check Amazon).<br></div><div><br>=
</div><div>You may need to drill the hole a bit deeper (with the drill mean=
t for the heli-coil) so that the tap can reach in far enough.</div><div>A s=
ide benefit is that the=C2=A0 heli-coiled thread in pot metal will be stron=
ger than before.</div><div><br></div><div>Also, a 1/4-20 coarse-thread scre=
w would come loose more easily=C2=A0 than a fine-thread one.</div><div><br>=
</div><div>Doug<br></div><div><br></div><br><div class=3D"gmail_quote"><div=
dir=3D"ltr" class=3D"gmail_attr">On Sun, Jan 15, 2023 at 10:54 AM john <=
;<a href=3D"mailto:jniolon@att.net";>jniolon@att.net</a>> wrote:<br></div=
><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border=
-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<div><font face=3D"Segoe UI">I have a mirror mount on my truck door that he=
ld a rear view mirror.=C2=A0 Unfortunately the mirror decided it didn't=
want to stay with my truck.</font></div>
<div><font face=3D"Segoe UI">So, I'm looking for a replacement. The mou=
nt is drilled and tapped for 1/4"-28 threads and most of what I find i=
s 1/4-20.=C2=A0 I'm wondering if I can</font></div>
<div><font face=3D"Segoe UI">re-tap the metal over existing threads with a =
1/4-20 thread and it will hold...or will I just make a mess of it and make =
it broke. The drill side for the</font></div>
<div><font face=3D"Segoe UI">two thread sizes are within a 64th or so of be=
ing the same and=C2=A0the mount is 7/16" or so wide so I have some mea=
t to play with...</font></div>
<div>=C2=A0</div>
<div><font face=3D"Segoe UI">suggestions?</font></div>
<div>=C2=A0<br>
</div></div></blockquote></div></div>
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