The Stovebolt Site Forums The Shop Area Paint and Body Shop What size are seat track bolts?

I'm trying to use some of the existing seat bolt holes in the floor of my 1957 Panel Truck. Am I correct that they are 5/16? Thanks in advance.

I am guessing noone here knew the answer, so I went to HD and bought some 5/16" bolts. The diameter is right, but they won't thread in, so I'm assuming they need to be fine thread. Hope this helps out someone else!

I am at a total loss here. Tonight I went to a True Value store that was 30 min from my house, and they had 5/16" fine thread bolts. I was ecstatic, and bought 8 of them. I come home, try to put one in the holes, and it still will not thread in. Can someone please tell me what I am missing here? I'm going to end up having to punch holes through the originals otherwise.

I also checked the assy manual, and I'm not seeing any specific bolt size in there, either. Why does this truck have to give me so much trouble??!!

Is there a part number in the FAM for the bolts you're looking for? If so, you might be able to use the Parts Catalog to determine the correct size.

Don’t own a panel, but are you sure the bolt hole threads don’t just need to be cleaned out with a tap?

I reached out to LMC. They replied and said the bolts are actually coarse thread, not fine, but are not telling me the bolt size.

Since I already tried a 5/16" coarse bolt, maybe I'll pick up the next bolt size down which I believe is 1/4" and give it a try. This is crazy!

This is just hilarious..

Popped a 1/4" bolt in the hole, it's too small of a diameter.. I bought some more 5/16" coarse thread bolts, and tried one in a different hole, it went in about 2 threads and stopped. I know the bolt hole size can't be metric, because cars in 1957 didn't use them. This is the craziest thing ever!

I guess I will proceed with punching new holes, which really bothers me, to be honest. I know I'm not restoring the truck to original, but I like to try to use original holes and connectors when I can. The seats I am installing only match up to one original hole any way, but this is still driving me nuts that I can't solve this mystery!!

The threaded portion of the holes are probably full of paint, rust, whatever. Were there bolts in them previously, or were they open to road gunk? I would run a 5/16 coarse tap thru them and move on.

1. "Chasing" the threads of an old truck is mandatory. Every threaded hole, every bolt.

2. There is a serious problem with "new" bolts and nuts. Been fighting it for years. Low quality plating. Meaning: too thick/too Chinese. At the slightest hint of tightening up during threading, you must stop and chase the new threads three times. Do the male and female with the same tap and die set. It must go together mostly by hand. Chase the original truck threads first. They do not have an additive style plating (more of a treatment), their only issue is built up rust and grime. That will be cleaned up by re-threading gently (chasing). If there is an "interference" after that, you know its the new stuff. If it won't thread in, throw it away and go to a different hardware store.

3. You should be able to tell fine from coarse from looking down the hole as well as size. Learn to do that if you want to get your gear head card.

Thanks, all- something's definitely up here (aka wrong threading, etc).

I've never had to do chasing or tapping before, so all of that's new for me.

As for the questions re: dirt in the threads etc, it has a mild dusting of primer on them, but I didn't see any real "dirt". Also, as they are interior holes, I could see the possibility of there being *some* dirt or corrosion, but I wasn't expecting this!

Also, re: the question about seeing the difference in threading between coarse and fine, normally, yes, I can distinguish between the two- but, these holes are small, and the threading starts a bit further in, so it's a bit hard to tell for sure.

And re: my "gear head" card, I should have earned that already, as I put an entire 1966 Chevelle back together from the ground up, myself. And during that project, I did not need to tap or chase a single bolt hole! This is just da** wacky!!

Lastly, I can see where a prior owner apparently tried to cut out this raised support for the seat mounts. I can't really understand why they did not follow through. It's only on the edges, so for all I know, maybe they were like that from the factory that way? I'll have to get a pic and post it.


Many many thanks for all of the replies, and I'll keep at it.

There were no bolts in the holes when I got the truck.

Well no clue when I picked these up, but I remembered that I actually do have a tap set in my toolbox (yay!). The 5/16" bit is in there, so I will give it a shot later today. I don't think I've ever used the set!

Get used to it! We need those taps on our old trucks. When you do get to it, use some oil, penetrating or WD will work, proceed slowly, making sure your tap is perpendicular to your hole, turn it in a 1/4-1/2 turn then back it out the same. Then turn it in an additional 1/4-1/2 turn and back it out and repeat until it runs free. If you feel any hard resistance, stop and access the situation. The last thing you want to do is snap off a tap in the hole. Then you really created a mess.

Now, a 5/16-18 tap is a bit more rugged than say 1/4-20, and I don’t really foresee you breaking that tap just cleaning out your threads but I just want you to be aware of that possibility.

Phil, they actually do make tools that will clean threads that aren't a tap or die. This way you don't cut material away, just clean what is there. Pictured is the low budget versions.

Thanks, guys!!

Since I have the taps already, I'll stick with them on this go-round. But man do I feel better about this whole debacle!!

YOU GUYS ARE THE KINGS OF THE DAY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Literally the MINUTE I was done work, I ran out (in the rain) with my tap, and started working on those holes from H3LL!! I have no idea how long they have been without a seat over them, but every single one of them had some kind of crud. I am proud to say that there is no permanent damage to any of them, and I can now use them ALL, successfully! I'm not installing an original seat in the truck, but it's nice to know that I can leverage the original holes for the adapters I will be using.

I will be uploading a pic momentarily, but I can tell you that if I had all of you in front of me right now, I'd be honored to shake every single one of your hands!!! This has been such a PITA!!!

Thanks,

Jim

Here are the holes with the new bolts in them:

As a career machinist I use taps. Lots of them. Starter, Plug and Bottoming. To get them started in the thread so you don’t cross thread them, I try to clean out the first thread with a pick. I’ve had pretty good success doing it this way.

I have made cleaning taps by cutting a slot on both sides, in line with the length of the bolt to allow the crud someplace to go.

Great news!

You all know you can take a common bolt with the proper threads, cut a slightly angled slot in the threads from bottom to top and make yourself a thread chaser in just a few seconds, yes? I have several of these around and I always try to use a new bolt to make one if I can.

Nope, did not know that!