Grade 5 or grade 8 bolts for seats and tether anchors?

[musigenesis]

The base of my seat is mounted to its pedestal with nine 2" 3/8 bolts. I'm going to get all-new hardware for this, since the original bolts are a bit corroded:



I can't tell if this is a grade 5 or a grade 8. What type would normally be used for this purpose?

I also will need to weld in new anchors on the floor for securing the seat belt tethers. These will involve 3/8 bolts (one for the tether on each side) coming up through a hole in the floor, with the heads spot-welded on the underside. Should these two bolts be grade 5 or grade 8? Are there any issued with spot-welding the heads in terms of weakening the bolts?

Lastly, I'm going to be bolting on the rails for my Ford transit van seat on the right side behind the stepwell. There are three bolts per rail and I was planning to use 3/8 here as well, but the holes in the rail could fit larger bolts if that's a good idea; also wondering about grade 5 vs. 8 for these. There will be additional structural pieces for the seat that will also be bolted with 3/8 hardware.

When I rebuilt my floor in the back, I used 3/8 grade 5 bolts in addition to welding, and I'm very comfortable with using this size and type of bolt (have the bits and sockets for it etc.). But I'm not putting my life in my hands with the floor rebuild, whereas with anything related to how the driver seat is attached to the bus, I am, so I'm looking for advice.

[EastCoastCB]

Grade 5 is what I've always found when pulling seats.

[JDSquared]

It looks like it has three lines on the top. Slightly raised so you should be able to feel them. That would be a number 5 bolt wouldn't it? A number eight bolt has five of those lines.

Unless I'm remembering completely wrong. I took my swivel seats out of my Econoline 2 years ago. Took the bench seat out of the back and replace the bolts after I put new flooring in. That's when I first learned about the lines and I'm pretty sure I had number five. But I will check when I get home later. My rear seat belts attached to this 4 ft channel piece which bolted to the floor of the van. Those were all the same bolts also.

[banman]

https://www.nutsandbolts.com/v1-bolt...-markings.html

[TheArgobus]

What the law says about seat belts: https://www.law.cornell.edu/cfr/text/49/571.209


What my summary was when I added seatbelts:

• Seat belt bolts must be at least 7/16" in diameter, 20 threads per inch, Grade 5 or 8 (this would be annotated as 7/16-20)
• Lap belt bolts must be secured with a 1.7" diameter washer
• Lap belt mounts should be spaced 16.5" apart, depending on comfort and space for your seat
• The top shoulder mount must be strong enough to withstand 7kN of force
• The bottom shoulder mount must be strong enough to withstand 14kN of force
• The buckle mount must be strong enough to withstand 12kN of force

And I am sure you know not to mount any seatbelts/seats to the bus chassis.

[banman]

Originally Posted by TheArgobus

What the law says about seat belts: https://www.law.cornell.edu/cfr/text/49/571.209


What my summary was when I added seatbelts:

• Seat belt bolts must be at least 7/16" in diameter, 20 threads per inch, Grade 5 or 8 (this would be annotated as 7/16-20)
• Lap belt bolts must be secured with a 1.7" diameter washer
• Lap belt mounts should be spaced 16.5" apart, depending on comfort and space for your seat
• The top shoulder mount must be strong enough to withstand 7kN of force
• The bottom shoulder mount must be strong enough to withstand 14kN of force
• The buckle mount must be strong enough to withstand 12kN of force

And I am sure you know not to mount any seatbelts/seats to the bus chassis.

Yup. As an aside -- I was looking at some inexpensive seat belts on ebay and sent a note to the seller: "were these belts in compliance with FMVSS 209...?"
The reply was "we're working on getting those certifications..."
I WON'T be buying those belts -- a very poor place to save $50...

Also, general rule for any given diameter bolt -- fine thread is stronger than course thread in tension.

[musigenesis]

Interesting: looks like my original bolts are Grade 8 (they either have the six lines or they have three lines and some random accidental marks) but they're definitely 3/8" (and not 7/16"), as were the bolts anchoring the tethers. I think the tether bolts were an after-market modification by previous owners, since the floor had other holes an inch away from the current bolt placements. The seat platform is also new (I think) so maybe whoever did this didn't know they should have used 7/16".

I'm inclined to just go ahead and use 3/8" Grade 8 for everything, since I'm forced to use that on the seat base anyway. I haven't found anything on what size bolt you're supposed to use on the Ford transit ban seat brackets, except one post that said 12 mm is the recommended bolt size (closer to 1/2").

Perhaps the thing to do is to use 1/2" Grade 8 for the transit seat brackets and for the driver's anchor tethers, and 3/8" Grade 8 for mounting the driver's seat base and also for the additional structure to support the transit seat brackets.

[EastCoastCB]

IIRC the federal regs for bus construction call for "grade 5 or 8". IDK. I wouldn't worry over it.

[Phatman]

Originally Posted by musigenesis

The base of my seat is mounted to its pedestal with nine 2" 3/8 bolts. I'm going to get all-new hardware for this, since the original bolts are a bit corroded:

Attachment 43293

I can't tell if this is a grade 5 or a grade 8. What type would normally be used for this purpose?

I also will need to weld in new anchors on the floor for securing the seat belt tethers. These will involve 3/8 bolts (one for the tether on each side) coming up through a hole in the floor, with the heads spot-welded on the underside. Should these two bolts be grade 5 or grade 8? Are there any issued with spot-welding the heads in terms of weakening the bolts?

Lastly, I'm going to be bolting on the rails for my Ford transit van seat on the right side behind the stepwell. There are three bolts per rail and I was planning to use 3/8 here as well, but the holes in the rail could fit larger bolts if that's a good idea; also wondering about grade 5 vs. 8 for these. There will be additional structural pieces for the seat that will also be bolted with 3/8 hardware.

When I rebuilt my floor in the back, I used 3/8 grade 5 bolts in addition to welding, and I'm very comfortable with using this size and type of bolt (have the bits and sockets for it etc.). But I'm not putting my life in my hands with the floor rebuild, whereas with anything related to how the driver seat is attached to the bus, I am, so I'm looking for advice.

I just extended the back bumper on my shorty, and all the bolts to the frame and bumper were all 1/2” grade 5 bolts.

[musigenesis]

{ snip ... }

Boy, it is a pain when you make a long post and then add it to the wrong thread.

[Ace Wilder]

Always use grade 8 for automotive applications, especially when it comes to seats and seatbelts. Grade 8 has way more tensile and shear strength than grade 5.

[musigenesis]

Originally Posted by TheArgobus

Seat belt bolts must be at least 7/16" in diameter, 20 threads per inch, Grade 5 or 8 (this would be annotated as 7/16-20)

Interesting, I decided on 1/2"-20 Grade 8 bolts for mounting my transit van seat (since the factory bolts for these are 12mm, apparently). I figured I would use the same for re-mounting my driver's seat tethers, but I just measured the hole on the floor bracket of the new tether belts I just bought and it's exactly 1/2", so I guess I'm supposed to use 7/16" for these.

Originally Posted by TheArgobus

And I am sure you know not to mount any seatbelts/seats to the bus chassis.

Oh yeah, I post that video a lot that shows the bus body sliding forward in a head-on crash. A seatbelt bolted to the chassis would be pretty grisly.

[somewhereinusa]

I buy bolts by the pound. I keep quite a few on hand. For the price difference it's not worth using grade 5.

[Gorzie]

I agree, the price difference between grade 5 and 8 is small. I went with a grade 8 bolts for any of my seats or belts. I tend to over engineer anyway. I would rather error on the safer side.

[Gorzie]

I forgot to mention I had some seat belts that are certified from seatbeltplanet.com . They are made I Oklahoma and are a veteran owned business if that make a difference to you.

[fignasiak]

I would use Grade 5 myself... unless I knew that what is being replaced was grade 8 originally. I forget all the proper engineering stuff, but it is not always better to use grade 8 over grade 5. Grade 5 may bend or stretch a little while a grade 8 might just break (although probably at a higher value).

[musigenesis]

Originally Posted by fignasiak

I would use Grade 5 myself... unless I knew that what is being replaced was grade 8 originally. I forget all the proper engineering stuff, but it is not always better to use grade 8 over grade 5. Grade 5 may bend or stretch a little while a grade 8 might just break (although probably at a higher value).

I've read this as well, and I agree it's best to replace what was there with the same thing. My seat was bolted down with Grade 8 bolts and I have an all-new set of these ready to put in. My seat belt tethers were screwed into the rotten plywood and rusty sheet also with Grade 8 3/8" coarse bolts, but I'm upgrading to Grade 8 7/16" for my new ones.

[solleks]

8 if youre the nervous type, 5 if u believe in God