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Thanks Corypad, so solve for Meff, THEN add 0.8P. I think I can back into the revised Meff eq from that, I think :)

Planning on red loctite

Can you elaborate on Helix Area. I don't understand what that is. Thanks!

Well, using Corey's formula, UTS = 45000psi or 310MPa C1 Dilation factor = 1 (not a nut, hole in relatively large area) C3 = .897 (don't know why for sure) Thread major diameter (of nut) 2.9mm Thread pitch 0.5 Meff = 4mm I get an A-shear area of 0.04291 in2 or 27.689 mm2 I got Fmax-nut =...

re Unbrako's chart, and making the assumption that metric will be the same as their UNC? thread tests for #0-#10, taking the conservative case of 1xD for depth (3mm), I get a conservative 170,000psi for Alu (doesn't say what kind of Alu). Converting to inch I get a strength of a M3 hole 1xD in...

Yes, Googled extensively before asking here. All of those links drive at the minimum threads to equal the strength of the same material fastener, where teh fastener will fail first. Or in one case a different material factor. One promising link in #1 above doesn't actually go where it says...

Thanks, worrying I did go look and cam to the same conclusion. Environment will be residential, dry, so no electrolyte.

CoryPad: At the end of that thread there is a discussion about the "addition of 0.8P to meff". Can you elaborate on that, or show me the equation with that added? It's not clear to me how to incorporate. Or if I am supposed to. Ashear,nut = (π d meff)/P · [P/2 + (d - D2)/√3] substitute...

Thanks Chris. Without going into the details, I'm basically having to check someone else's design/part to be sure it meets my expectations. I've got some, but pretty limited input on the details. I'll be doing good to get form threads. So helicoils probably aern't gong to happen. My hope is...

Thanks CoryPad, I'll digest that thread and see if I can do the calc.

hmmm, that's not good, I'll do some research on that. Thanks.

Branching this thread to the ME area, where I meant to put it in the first place (Still no sure how it ended up here, oh well...) Moved to: http://www.eng-tips.com/viewthread.cfm?qid=362988

It's been a long time since I had to do anything like this and my old ME training is rusty. I need to determine the tensile strength for a threaded hole. As the hole is under the normal rule-of-thumb depths for full bolt strength, AND the material is weaker than the bolt, I figure the weak link...

Thank you. I've looked at that, but about half way through it it goes to being sure the screw fails first: "To ensure that the screw fails before the thread strips it is necessary the the shear area is at least 2 times the tensile area." Stupid me, I thought I WAS in the ME area, not sure...

I'd like as much safety factor as I can get. So I'd prefer to work it the other way. i.e. How much strength do I have then determine how much safety factor I have based on what would be applied.

I'm OK with stainless, but it's not as strong. If I can determine the strength of the threaded hole and it's less than a SS fastener, then I'm all for it. FWIW these are not in a corrosive environment and I can use some anti-corrosive measures on the steel if necessary. Unless it's some sort...

None of my books address it. Everything wants to default to the rules of thumb i.e. 2xD for dissimilar materials to achieve tensile strength of the screw. Don't have that luxury, I'm limited on thread engagement.

It's been a long time since I had to do anything like this and my old ME training is rusty. I need to determine the tensile strength for a threaded hole. As the hole is under the normal rule-of-thumb depths for full bolt strength, AND the material is weaker than the bolt, I figure the weak...

Understood. Thanks. I had it right all along. Just wanted to be sure.

OK, from memory then. Using the units that after cancellation left me with what I wanted. But as I wasn't sure by any stretch, and was compelled to ask, so certaitnly a little unwit <big grin>.