3-point seat belts: dimension of top bolt?

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3-point seat belts: dimension of top bolt?

Postby Florian on Sat May 29, 2010 4:57 am

Hi!

I bought a 3-point seat belt conversion kit for my 71 F100. The bolts delivered with the set won´t fit in the upper mounting hole. Since we have the metric system over here it´s quite difficult to get one of these bolts. I need to know the dimensions of the bolt that goes in the upper mounting hole then I can order the two bolts.

Thanks!
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Re: 3-point seat belts: dimension of top bolt?

Postby robroy on Sat May 29, 2010 12:53 pm

Good day Florian!

I'm not sure whether you've glanced at my ongoing seat belt thread:  May I ask for advice on Beam's 140" WSCH300 seat beats?

Your question remains my unsolved mystery as well, yet I've gathered these facts:

     
  1. Some trucks came with those shoulder anchor inserts pre-threaded, while some require threading.
     
  2. VernF110's 1969 F100 4x4 came with the inserts pre-threaded with 3/8-24 threads.
     
  3. The 3/8-24 threads on Vern's truck fit a 3/8-24 bolt in a nice and tight fashion; they weren't loose at all.
     
  4. I ran a 3/8-24 tap through one of my inserts, yet the fit of a bolt in there feels loose, as though its beginning diameter was too large for proper 3/8-24 threads.
     
  5. 70_F100 mentioned that he'd check the status of the shoulder anchor inserts on his '70, to add another data point.
     
  6. The 1972 Ford Truck Shop Manual seems to claim that the bolt's supposed to be a 7/16-20 bolt, not a 3/8-24 bolt.

Since I tapped one of my 1972 inserts with 3/8-24 and it seems a little loose, I'm probably going to have to drill it out slightly and re-tap with 7/16-20 threads.  At the moment I'm at a stand-still though, focusing on other things, and anticipating the results of 70_F100's truck inspection!

Florian, is there a local store where you can buy one 7/16-20 bolt, and one 3/8-24 bolt?  These are fine-thread bolts, and just to be certain they're strong enough, you'll probably want to buy grade eight (six lines on the bolt heads).  If you bought these two bolts, you could test them in your inserts to see which one's the correct thread.  

Yet perhaps before that, are you sure your inserts are currently threaded?  Some came threaded, while others did not.

Florian, I hope you're having a great weekend!
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Re: 3-point seat belts: dimension of top bolt?

Postby garner67 on Sat May 29, 2010 3:32 pm

My 71 XLT Ranger has bolt holes for shoulder harness mounts.  The holes for the shoulder mount are 3/8 diameter with a 24 tread pitch, but the seat belt bolt holes in the floor board are 7/16 diameter with a 20 thread pitch.  

After removing the plug for the shoulder mount hole, I ran a tap the clean out the threads, now a 3/8 - 24 bolt fits perfectly.  The last thing to do is sort out how I'm going to attach the seat belt retractor on the floor board.  I think I'm going to make some brackets from 2" angle iron.
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Re: 3-point seat belts: dimension of top bolt?

Postby fordman on Sat May 29, 2010 4:11 pm

the bolt holes usually arent pre threaded. yo uhave to tap them yourself. if the bolts you have are to big to use at all. i would go to a junkyard and get the bolts that will fit so you dont have to buy american made tools to tap out the hole with.
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Re: 3-point seat belts: dimension of top bolt?

Postby Florian on Sat May 29, 2010 4:17 pm

Haha this is crazy  :lol:  

Mine are already threaded! I think I´ll do it like you said, robroy, and buy both bolts and test which fits better.  :thup:
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Re: 3-point seat belts: dimension of top bolt?

Postby Florian on Sat May 29, 2010 4:40 pm

I just found a site that explains the american bolt dimension system, so did I get this right, I need either 7/16" - 20 UNF x 1" or 3/8" - 24 UNF x 1" bolts? One inch long should be enough or? Or better a bit longer?
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Re: 3-point seat belts: dimension of top bolt?

Postby fordman on Sat May 29, 2010 5:03 pm

soemone who has these bolts out of a parts truck should be able to send them to you. i dont think i have any but i mihgt have. i dont have time to look. im getting ready to leave.
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Re: 3-point seat belts: dimension of top bolt?

Postby Florian on Sun May 30, 2010 3:47 am

Yeah but the cost of shipping just the two bolts to Germany would probably be double or even more than just buying four of these bolts over here, but thanks anyways!  :fr:
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Re: 3-point seat belts: dimension of top bolt?

Postby fordman on Sun May 30, 2010 3:52 am

i know what you mean. i just didnt have an answer for you about the metric sized bolts.
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Re: 3-point seat belts: dimension of top bolt?

Postby Florian on Mon May 31, 2010 1:05 pm

Got the 7/16" bolt today, but they were way too large. Gonna need to order the 3/8" bolts..
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Re: 3-point seat belts: dimension of top bolt?

Postby cep62 on Mon May 31, 2010 6:42 pm

Couldn't you just tap them to 12.mm?
and use easy to find bolts?
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Re: 3-point seat belts: dimension of top bolt?

Postby Florian on Fri Jun 04, 2010 1:26 pm

Yeah that´s what I did. 10mm. Fits fine.  :thup:
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