Odd size bolt ?
 

I have a 72 blazer and nee the two hold down bolts for the floor dimmer switch. I have one actually and it seems to be an odd size thread.

Thanks,
Bret

They should be 1/4" - 20 with a phillips head.

I have tried both 1/4 20 and 1/4 24 with no luck. The one the PO did have was wrong as well, the reason it was loose.

1/4"-20 is National Course thread. 1/4"-24 is National Standard thread. 1/4"-28 is National Fine thread. The only time I've seen National Standard used was on a top cover for a Harley 4 spd. Not a real common size anymore. Take the one you have and go to a nut and bolt house. They should be able to help?

:flag: :gmc: :burnout:

As gonebad2 stated the screws that were originally on the dimmer switch are 1/4-20 x 1/2" phillips head screws.

Have you tried chasing the threads with a 1/4-20 thread chaser or tap.?

JIm

Re: Odd size bolt ?
 

Did you ever figure this one out? I have the same issue on my ‘69 c10.

Re: Odd size bolt ?
 

After 17 years, I'm sure he did "figure it out".. Regardless of what fasteners you have, the correct fastener is a phillips head 1/4" X 20, 1/2" long... As was stated in that old thread. chase the threads in the hole with a 1/4' x 20 tap before installing the new fasteners...

Re: Odd size bolt ?
 

Sometimes this area gets a lot of rust. This can cause the threads to pull when the original bolt is removed. If they are too loose you have a few options. Drill it out for a well nut. Using a version of a pop rivet gun to install an threaded insert. Or weld it up and re-drill. Not a lot of room to go up a bolt size. Don't forget the bent tab that retains the wire for the dome light that goes on the outside bolt. Cheers.
Rick

Re: Odd size bolt ?
 

Thanks guys, didn’t notice the date on this thread. I was just happy to see I’m not the only one. Lol. The factory size on my truck wasn’t standard, learning that about this truck all the way around.like maybe some corners were cut. The hole & threads are actually larger than stated so I’ll go through our odds and ends and see what I come up with. No rust in that area thankfully.

Re: Odd size bolt ?
 

Some thoughts...if the threads are gone beyond repair, you could drill and tap to the next size up. This might be, day I say, need to be a metric bolt to get the next size up without over drilling the weld nuts below the floor. You would just have to see what size hole can be drilled into the weldnuts without getting too close to its edges. Another thought, IIRC, you can access the dimmer holes from under the cab and could just put smaller bolts through the holes from above and use nuts below. Not factory and not as easy to change out, but not a big deal either.

Re: Odd size bolt ?
 

I would do like sick472 suggested get a 1/4 x 20 Philips head bolt and put a nut under the cab and use lock tight on it. That way it would look original.

Re: Odd size bolt ?
 

And that repair will probably last 50 years, too!