MTFCA Forum

Here we go with that firewall again. The drawing shows ⅜" holes for the two bolts and calls for T-7255 body bolts without giving the bolt size. The bolts used when this car was assembled in the seventies are ⁵⁄₁₆". I'm assuming that the ⁵⁄₁₆" bolts are wrong and they should be ⅜" , but I'd better check and be sure. I've found plenty of incorrect parts in this car, and I figure these are most likely two more of the same. I have the drawing for the firewall, but not for the hood former.

I vote for the 3/8” carriage style bolts. I say ‘style’ because the dome head is much greater diameter and flatter than hardware store carriage bolts. And the nut on the interior is square. I may have 2 of these if you don’t. Will gladly make them available.

I'm surprised to see a 3/8" hole there. I have always assumed it was a "step" bolt that went there, 5/16". This is what I believe the bolt is. It is 5/16" by 1 5/16 log. The head is 1 1/16 dia. The square hole in the hood former is 11/16". A 3/8 would be too large for it. The square shoulder on the step bolt is a bit over 5/16" so it would fit there nicely. I have drilled that hole 5/16 match drilled at assembly. 3/8" hole might have been used to give some clearance for easier assembly. Things don't always line up.
I'll see what more I can find.
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Rich

The "I think" originals I used on my 1915 runabout were 5/16. And I am fairly sure the larger 3/8 bolts would not have fit in the sheet metal holes.
Pure speculation? Perhaps the hole in the wooden firewall were 3/8 because a little "wiggle room" was needed because the sheet metal and wood did not always line up exactly?

Tried looking up the dimensions of that part, factory T-7255, and the only ref. is 1912 Price list, p/n 3653, that one is 1/4" x 1 1/4" x 20 thrd.

The later books have the p/n 3653B, so there was a design change. Suspect that the bolt is a carriage bolt, with the size head of a carriage bolt that dia. In early days carriage head were nice and large, of course the typical 'step bolt' has more of a flatter head.

Looking at bolt styles, the 5/16”dia. seems suitable to a head shape seen in old photos of original cars for the hood former.

The 3/8" hole is likely needed to clear the square shank under the bolt head. I have never seen anything other than 5/16 " bolts in ANY T model firewall. On my 1915 tourer the original bolts were almost rusted away when I dis-assembled it. I made the large flat heads on the replacement bolts by bronze welding washers under carriage bolt heads and turning the profile in the lathe.

Hope this helps.
Allan from down under.

One of my '15/'16 hood formers had the remains of an original bolt in it. It was rusted about half gone, the head in poor condition, the shank and threaded portion barely hanging onto half missing square nut. There was a short piece of threaded area underneath the nut that was intact enough to identify it as 5/16.
In a box of mostly model T small miscellaneous and hardware, I had two nearly identical bolts in almost good condition. A little repair work and those two I used on my runabout.

I know there is a proper name for those large head carriage type bolts? But google did not want to remind me what it is. I believe "step bolts" may be correct.

Step bolts it is.

https://www.aftfasteners.com/step-bolts ... oft%20wood.

Art Bell posted this chart back in 2010. The thread also has carriage and elevator bolt charts. http://www.mtfca.com/discus/messages/11 ... 1288281081
The step bolt dimensions are very close to the rusty one I showed earlier.
I ended up using carriage bolts in my two '15s. I soon forgot and nobody has mentioned them to me.

Bob Bergstat (Bob's Auto Parts) had those big-headed carriage bolts a while back. He may still have some.

Here you go. Someone could buy them and sell them separately.
I tried that with #8-36 throttle arm screws and didn't get many takers but I'm sure this is different.

This is all I have left out of over 2000 bolts, Bob