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I'm not understanding your post #39 where you say the seatbelt bolt fit the hole in the car, you then brought that to Lowes and it was a proper fit at lowes (though you say as of that writing you 'don't know' it's size?), though tight. Eh? If you found the seatbelt bolt fit the hitch hole, then that's the proper size, right?

On metric - I don't think you'll find anything that's SAE on the Supra. It's a metric car. So be careful you are not screwing the proper size bolt into a rusty set of threads on the frame and concluding you need a different size. I'd be shocked if you found an SAE fastener there, though the Japanese have always been deathly afraid of US liability and towing and hitches are the scariest. So who knows - they may have put US only fasteners there compatible with US hitch makers (possibly all SAE in the 80s...). Proceed with caution. Be sure the car's threads are clean down under there for 30+ years.
 

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I'm not understanding your post #39 where you say the seatbelt bolt fit the hole in the car, you then brought that to Lowes and it was a proper fit at lowes (though you say as of that writing you 'don't know' it's size?), though tight. Eh? If you found the seatbelt bolt fit the hitch hole, then that's the proper size, right?

On metric - I don't think you'll find anything that's SAE on the Supra. It's a metric car. So be careful you are not screwing the proper size bolt into a rusty set of threads on the frame and concluding you need a different size. I'd be shocked if you found an SAE fastener there, though the Japanese have always been deathly afraid of US liability and towing and hitches are the scariest. So who knows - they may have put US only fasteners there compatible with US hitch makers (possibly all SAE in the 80s...). Proceed with caution. Be sure the car's threads are clean down under there for 30+ years.
Yeah I should have been more clear on that. I took the seatbelt bolt to lowes and tested it on their bolt sizer. The only size it really fitted in metric was the m12x1.25. Got a couple m12x1.25 and it's too large for the hitch mounting holes. This is the reason I'm wondering if it is SAE as I didn't test the seatbelt bolt with the SAE sizer. Thats the meaning behind I don't know the correct size.

And I do find it funny how toyota says don't tow with the supra yet they put the mounting holes for a tow hitch on the reinforcement bar. Was there bike racks back in the 80's that could have been used and they meant not to tow trailers or other vehicles?
 

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Do not use bolts from Lowes here, even if they have them. My go-to for this type of hardware is McMaster-Carr. Fastenal is another option, especially if you can go to one of their stores.

While it's been forever since I played with my hitch, I am 100% sure the bolts are metric. There absolutely are no SAE bolts in this car. Most are JIS, which is somewhat obsolete today, but you can still find them. The nuts are already welded inside the bumper bar. I figure Toyota used the bumper bar in another car they thought ok for towing.

In fact, Curt's instruction sheet says the 4 bolts are M12x1.25, 40mm long, grade 10.9, yellow zinc finish, if I'm parsing that right.

Metric 10.9 is roughly equivalent to SAE grade 8. Metric 8.8 is roughly SAE grade 5.

A fine-thread 1/2-20 SAE bolt is close to an M12x1.25. If the size checker is not that great it probably would fit either, even though they really are not interchangeable.

If you can, inspect the thread in the bumper with a bright light and mirror. I can only imagine them being rusty so fitting new bolts won't seem right even if they are.
 

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Do not use bolts from Lowes here, even if they have them. My go-to for this type of hardware is McMaster-Carr. Fastenal is another option, especially if you can go to one of their stores.

While it's been forever since I played with my hitch, I am 100% sure the bolts are metric. There absolutely are no SAE bolts in this car. Most are JIS, which is somewhat obsolete today, but you can still find them. The nuts are already welded inside the bumper bar. I figure Toyota used the bumper bar in another car they thought ok for towing.

Metric 10.9 is roughly equivalent to SAE grade 8. Metric 8.8 is roughly SAE grade 5.

A fine-thread 1/2-20 SAE bolt is close to an M12x1.25. If the size checker is not that great it probably would fit either, even though they really are not interchangeable.

If you can, inspect the thread in the bumper with a bright light and mirror. I can only imagine them being rusty so fitting new bolts won't seem right even if they are.
So here's what I found. A 7/16-20 fit perfectly snug in the holes which is weird since as you said this car is all metric. On the other note as you said the threads are pretty rusted so I don't feel comfortable torqueing these down to 86 ft-lbs as the installation guide for the hitch requires. Here's what im considering. Getting one of these hitch hardware kits to feed the bolt though the mounting points to get better torque. What do yall think?
Rectangle Font Circle Auto part Number
 

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Your 7/16-20 has a thread pitch of 1.27mm, which is very close to 1.25mm. 7/16" = 11.1mm, which is smaller than 12mm, enough that it'll fit with the rust in there. I can easily believe a 7/16-20 fits nicely by hand. I wouldn't torque it down, though. You'll surely strip out the nut.

I personally would clean the threads and do my best to fit M12x1.25 bolts. DM has the tap for $8. If you want to get really fancy, ARP has a thread chaser tap that's a little small meant to just clean threads in a block, but it's $38 at Summit.
 

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Your 7/16-20 has a thread pitch of 1.27mm, which is very close to 1.25mm. 7/16" = 11.1mm, which is smaller than 12mm, enough that it'll fit with the rust in there. I can easily believe a 7/16-20 fits nicely by hand. I wouldn't torque it down, though. You'll surely strip out the nut.

I personally would clean the threads and do my best to fit M12x1.25 bolts. DM has the tap for $8. If you want to get really fancy, ARP has a thread chaser tap that's a little small meant to just clean threads in a block, but it's $38 at Summit.
Understood, will get a thread chaser and clean up the threads. M12x1.25 bolts will be used.
 
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Took off the rear reinforcement bar and will be taking it to a machine shop to have the threads professionally tapped. Would rather be safe then sorry when it comes to towing. Will be taking the bar in on Monday.
 

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FWIW:
My son took this photo at the track today. Son said three tires on the hitch cargo carrier and the 4th tire inside the car.
I went to check it out but the owner has left. I have a feeling that the car had a class 3 or 4 hitch since that looks like 2" square tubing under the carrier..
(I think this might have been what IdahoDoug was referring to.)

Tire Jeans Wheel Car Vehicle
 

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FWIW:
My son took this photo at the track today. Son said three tires on the hitch cargo carrier and the 4th tire inside the car.
I went to check it out but the owner has left. I have a feeling that the car had a class 3 or 4 hitch since that looks like 2" square tubing under the carrier..
(I think this might have been what IdahoDoug was referring to.)

View attachment 265769
I kinda doubt they would have a class 3 or 4 hitch for a tesla car. I see they have 1.25" to 2" hitch adapters on the market. I would assume they used the adapter for the hitch for those rear racks.
 
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