Is it okay to replace fine thread frame bolts with coarse thread?

[belfert]

Some of the radiator framework in my bus is held down with fine thread flanged frame bolts.  I lost two of these bolts somewhere along the way.  Hardware stores and auto parts stores only have the coarse threaded version of these bolts.  I've tried MCMaster-Carr, MSC, and Fastenal to no avail.  There are lots of places online that have these, but I would have to buy between 100 and 1000 of them.

Am I going to have issues going from fine thread bolts to coarse thread bolts?  The bolts are 1/2-20 now.

[maria-n-skip]

  I am suprised NAPA doesn't have fine thread bolts. Some of our hardware staores have a good selection
of bolts if you don't need anything harder than grade 5.  The Cat dealer in most areas have a good selection
  of grade 8 bolts. (and FINE thread is used quit a bit)

    To use coarse you should retap and at best it will be a poor hold factor.


    FWIW
Skip

[FloridaCliff]

Brian,

Call a long established hardware store.

I have two old style stores in my general area and they carry everything.

New blister pack stores don't come close.

Cliff

[belfert]

The bolts go through the frame, not into it.  There is a nut on the end of the bolt.  Some places call them frame bolts and others just call them flange bolts.

The bolts are grade 8 flange bolts.  The nuts also have flanges with no washers used.  Finding fine thread grade 8 bolts is not an issue.  The flange part is the issue.

I've been to several old fashioned hardware stores and a few auto parts stores and they only have the frame/flanged bolts in coarse thread.  I did think of one other hardware store that might possibly have them, but not sure I want to drive all the way over there.

[maria-n-skip]

Try these people


Fastenal Co - more info »
7521 Washington Ave S, Edina, MN
(952) 941-9566
Category: Nuts & Bolts

They report in stock    1/2-20 1.5 long grade eight


    Hope this helps

   Skip

[belfert]

Try these people


Fastenal Co - more info »
7521 Washington Ave S, Edina, MN
(952) 941-9566
Category: Nuts & Bolts

They report in stock    1/2-20 1.5 long grade eight

Do you have a Fastenal part number?  The web site when listing flanged bolts jumps from 1.25 inch to 2.25 inch.  I'm guessing most stores would not stock this, but I don't have a problem ordering the bolts.

The Fastenal website used to have catalog pages in PDF for each item, but not anymore that I can see.  I was hoping to look at the catalog pages to see if the website is just screwed up.

[maria-n-skip]

  Since I'm not sure of what length you need........

1/2-20x2 G8 FLG PO
Sku: 19831
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock Item  $1.01


1/2-20x1.5 G8 FLG PO
Sku: 19829
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock Item  $0.91


1/2-20x1.75G8 FLG PO
Sku: 19830
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock
Limited Locations  $0.96

1/2-20 x 2.5 Hex Flange Bolt Grade 8, Phos & Oil
Sku: 0142799
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock
Limited Locations  $1.49


1/2-20x1.25G8 FLG PO
Sku: 19827
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock
Limited Locations  $1.02


1/2-20 x 3 Hex Flange Bolt Grade 8, Phos & Oil
Sku: 0142801
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor Lead Times Vary  $2.16


1/2-20 x 2.25Hex Flange Bolt Grade 8, Phos & Oil
Sku: 0142798
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor Lead Times Vary  $1.40

IF you need something shorter than listed you can do an old trick of putting a throw away nut on then then cutting
it with a hand grinder clean up the end and back the nut off.....

Hope this is helpful

Skip

[Utahclaimjumper]

A flanged bolt is no different than a bolt with a flat washer, try washers and lock nuts.>>>Dan

[belfert]

  Since I'm not sure of what length you need........

1/2-20x1.5 G8 FLG PO
Sku: 19829
Package Quantity: 1
Manufacturer: Fastenal Approved Vendor In-Stock Item  $0.91

Thanks much.  The program on the Fastenal web site that helps narrow down the 400+ choices for flange bolts didn't show the 1.5" bolt.  I actually downloaded the entire catalog in PDF and was about to look at it.

I would much prefer to use the same bolts as original instead of trying something different.  The manufacturer probably choose flange bolts for a reason as I think they cost more than a bolt and washer.

[kyle4501]

Fine thread bolts are stronger than the coarse thread of the same size (due to the larger diameter at the root of the thread & other things). Is the joint highly stressed? Do you need all the strength of a fine thread? The manuf may have used them as a commonality thing, maybe purchasing screwed up, maybe the vendor was out of stock of the regular bolts & substituted a better bolt to make delivery, maybe . . . .

Does the flange/ frame bolt have serrations under the head? If so, this is a real help in reducing loosening due to vibrations. If it were me, I'd use standard grade 8 fine thread bolts with the all steel lock nut to eliminate the loosening issue ( I'd also use the GR8 flat & lock washers too).

[DavidInWilmNC]

Thanks much.  The program on the Fastenal web site that helps narrow down the 400+ choices for flange bolts didn't show the 1.5" bolt.  I actually downloaded the entire catalog in PDF and was about to look at it.

I would much prefer to use the same bolts as original instead of trying something different.  The manufacturer probably choose flange bolts for a reason as I think they cost more than a bolt and washer.

Brian, it sounds like you're caught between what you want to use and what's available.  You may have to use what's available.  You said you lost two.  How many are remaining?  I wonder if two bolts with washers would be OK, since you've got all the rest?  Perhaps the manufacturer used flanged bolts 'cause they're easier and quicker to install.  My MC-8 had them to hold the fiberglass wheel well liners in.  I can guarantee you that the washers and bolts I used will hold that fiberglass liner in just fine.  I realize you're talking about a heavy radiator, but with a grade 8 washer, bolt, and lock washer, I'm sure that radiator won't be going anywhere any time soon.  If you're still not sure, pop a small spot weld on each washer to the bolt and make a flanged bolt.  I can't see how this would be an issue.

David

[belfert]

The radiator support is bolted to the frame rail with six of these flanged bolts with flanged nuts.  Four are on the main support and two are on an angled brace welded to the main support.  Overkill probably.

I think I'll probably just use the coarse threaded bolts.  I still need to find the two nuts I dropped on the ground.  I will probably need a magnet to find the nuts as I crawled under there on my belly and could not find them.  I wish I had a nice concrete driveway instead of river rock, dirt, and leaves.

[DavidInWilmNC]

I wish I had a nice concrete driveway instead of river rock, dirt, and leaves.

I'll trade you!  I've got sand, a bit of dead grass, some leaves, and oil (it's a 2-stroke, remember!).  The worst is the sandy soil; my tires sink a couple of inches within a week or two!

Daviid

[Utahclaimjumper]

You guys are making me feel bad, Ive got a 40X45 garage with a spotless floor and still loose things.>>>Dan

[TomC]

For supporting the radiator, course will be fine.  I like to double or jam nut each bolt.  If it is a frame structural point, only grade 8 fine should be used.  Good Luck, TomC  PS-Home Depot has fine bolts and nuts.