MTFCA Forum

Does anyone have a guess what equivalent SAE grade the bolts used in the Model T would have? I'm asking so I'll have an approximate idea of the proper torque to use. Yeah, I know, "Don't need no stinkin' torque." Humor me if you can.

I have seen folks mention grade two in older posts.

I would tend to agree. A common grade two bolt will bend or flex for a long time, while a higher grade might fracture from stress. I suspect Henry's bolts were at least a little better than our modern grade two though, since he was a fan of vanadium steel in just about everything else. I've assembled most of my engine using grade five fasteners, but only because our local supplier only carries SAE thread in that strength. I won't consider anything harder because.....

Years ago, I used to pump water with an old hit and miss engine and a pump jack. The original connecting bolts that converted rotary motion to up and down were missing on the pump jack so, knowing everything, I replaced them with 3/4" grade EIGHT bolts. Not even a month later there was a terrific clattering sound and after I shut the engine off, I found that one of those bolts sheared off right at the start of the threads. The metal appeared to have a "crystallized" appearance at the break. Lesson learned: a softer bolt would have been better in a repeated stress situation than a hard one.

The general use bolts were all pretty much specified as Cold Drawn Bessemer Steel....with a few being specified as Type E steel, or Type N-K steel.


When digging deeper type E and Type N-K seem to be also Bessemer Steel in Fords own cross references so my guess is that these letters are not neccessarily reference to the Ford ferrous chart but rather to a given finishing process for the 'cold drawn' Bessemer steel. Somewhere I have a true listing of Ford actual finishing Processes for Metals...but danged if it wants to be found today!

Look at it another way...I'd be pretty certain that special finishing processes would not really change the tensile that much if at all, but would/could arguably increase the quality yield since BESSEMER of the era was actually cheap crap steel, sort of like A36 is considered today (It's sort of 1020...but not...lol).

Point? Without further understanding of what any special process might do and which I'd doubt, I'd rate BESSEMER of the era at 53-55,000 Tensile, 32-33,000 yield. This would put it down around the non-existent Grade 1 Bolt Category so present day Grade 2 would be the closest equivalent in terms of strength.

I had a kingpin tested and it came in less than but close to a modern grade 2 fastener.

Very helpful information... Kinda what I was thinking but it's good to hear that others have come to the same conclusion. Thanks!

Humble J..

Thanks for that comment. It confirms further my own thought. Spindle Bolts were by specification Cold Drawn N-X Steel.


I double checked my source and I have a typo above...there is no N-K, just N-X steel

There are at least 3 repro. spindle bolts available - did you check the "hardened & ground" one ?

Steve - I'm a bit confused by this most recent discussion,....I don't see anything to indicate that the spindle bolt that Jeff had "tested" was anything by on original Ford factory spindle bolt. Are you assuming that the one he had "tested" was one of the three "re-pops", or are you asking if a comparison was made between an original Ford factory spindle bolt and one of the re-pops,....????

Sorry,....not trying to confuse the issue here, but the comparison I just mentioned would be very interesting, and just might suggest another case whereby an original Ford part would be much more desirable that one of (....or even "all of") the new spindle bolts that are available from the major Model T parts suppliers,.....harold

Going back to my original statement, I don't think I'd want a "hardened and ground" spindle bolt...........unless the manufacturer can assure me that it's NOT hard as glass, or anywhere near it. Having a king pin break at 30 mph could really foul up your day! Basically, you want something "tough", but not hard.

Fasteners under stress or vibration have to have a little "give" in order to perform. The grade eight bolts available today are wonderful for holding two pieces together if they're relatively static. A pipe flange under tremendous pressure would be an example. If there is any repeated pounding or shear stress involved, I'd have my doubts.

Steve, my response to Tim was regarding original Ford kingpin hardness, not the new reproduction kingpins, and no, I do not know the hardness of the new kingpins.
The Ford drawing identifies the kingpin to be cold drawn, cold headed, wire type"N", and heat treated.
The Ford drawing for the crank shaft starting pin identifies the material as cold drawn, bessemer, screw stock (no heat treat noted).
So, different materials for kingpin and screw stock, kingpin tested just less than a modern grade 2 bolt. Ford bolts are still anybodys guess, but I am not going to speculate.

All good information - thanks !

I could be way off base here, but I think the term "hard bolts" is a bit of a misnomer. I think the higher grades are actually tougher, not harder. Just what I've heard over the years. Dave

Tensile strength.