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Take me to hardware school please

Take me to hardware school please

Take me to hardware school please

(OP)
I've been noticing on some outline and installation drawings for electronic equipment onboard a ship the specification of -2A bolts and -3B self locking nuts for hold-down.  The originator is not available to consult.

Are class 3 nuts typically used with class 2 bolts.  Why or why not?

Are grade 5 bolts usually class 3 or could they be class 2?

Thanks,
Dan

RE: Take me to hardware school please

Assuming you're talking UN threads...

Looked into this a while back up to a point, -2A bolts will work with -3B nuts.  The fit will be a little 'tighter'/more precise than 2A & 2B but looser than 3A & 3B.

Doesn't really answer your question though.  We use class 3 for a lot of fine adjustment screws, not sure this is applicable to your situation though.

KENAT, probably the least qualified checker you'll ever meet...

RE: Take me to hardware school please

(OP)
These are bolts to hold equipment racks on their foundations.  I knew the class 3 was a more precise thread but didn't know if there was an engineering reason that mixing them was somehow superior.

Meanwhile, I've found a Grade 8 class 2 bolt specified.  Is that one available?  I thought the stronger the bolt, the tighter you wanted the fit--thread bearing surface deformation and all that.

There's a lot of inconsistency in what I'm looking at because it came in parts from a dozen or so places.  I'm beginning to think the designers were no more qualified to spec hardware than I am.

Thanks again,
Dan

RE: Take me to hardware school please

Generally, class 2 are more common, from what I've seen since being in the states.  I  don't know for Grade 8 specifically.

Class 3 allow a line fit at max tol which doesn't work well with any contamination etc.

KENAT, probably the least qualified checker you'll ever meet...

RE: Take me to hardware school please

I ran into this same problem with prevailing-torque locknuts.  The Industrial Fastener Institute has specifications for locknuts (http://www.indfast.org/publications.php?cat=3) that call for the same class of fit on both screw and nut.  My conversations with application engineers at the prevailing-torque locknut manufacturers did not come up with an answer.  My application was used in a high-heat environment and the suspicion was that the class 2 nut and class 3 screw threads had something to due with thermal cycles.  The individuals who decided on the fit mis-match were very thorough, and just like you, they are not around to ask why.  Please post any findings you come up with.

RE: Take me to hardware school please

(OP)
I've found yet another scenario.  This one shows grade 8 bolts securing an aluminum rack to a steel platform.  Can you fully torque or pre-tension grade 8 hardware with aluminum on one side?

Dan

RE: Take me to hardware school please

What grade aluminium?

This site will allow you to get a ballpark stress figure if I recall correctly.

http://www.boltplanet.com/default.asp

KENAT, probably the least qualified checker you'll ever meet...

RE: Take me to hardware school please

"Can you fully torque or pre-tension grade 8 hardware with aluminum on one side?"

Certainly, with a wide enough and thick enough washer under the bolt head.

Of more concern to me is the (apparent) contact between steel and aluminum in a marine environment with no (apparent) concern for galvanic corrosion.

RE: Take me to hardware school please

(OP)
Kenat, 6061-T6.

btrueblood, we're inside in a well air conditioned space--very well air conditioned.

Dan

RE: Take me to hardware school please

With a grade 8 bolt and aluminum, you may need a larger
od washer to prevent embedding the washer into the aluminum if you are using the full clamping force of the grade 8 bolts.

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