metric screws and a/nuts ? 1

[rb1957]

Hi, we're designing in NA (the last hold out for the Imperial system) but are mounting a European antenna (for a plane to be operated in Europe) with metric holes (M5.5). I'm being told that there are very limited options for metric a/nuts (only clikbond). I want to call BS on this. Unless it is common practice in Europe to use imperial a/nuts with metric screws (which I find hard to believe).

Can someone comment please ?

Yes, helicoils are an option ... so we could make our own "a/nuts" ... a strip of Al with helicoils and interpitched rivets attaching strip to skin ... UGLY !

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

I'm aware that SAE has metric fastener specs... and there are metric Hi-Loks Pins/Collars too... I've just never used any parts except US In-# standard parts... sooooo I'm unsure of availability.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

Thx Will but your my side of the pond. I wanted to hear what they do over there. Thx.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[MintJulep]

M5.5?

Yes, it's definitely in the charts. But it's not common in reality.

 

[rb1957]

thx, which charts ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[MintJulep]

It's in ANSI/ASME B1.13M

But not ISO 724.

I use Fastenal as my test of "does it exist". They don't have nuts, hex head bolts of SHCS in M5.5. That's a good indication that it isn't common.

 

[verymadmac]

I guess A/nut means anchor nut.

About 15 years ago we had this problem, needed a single leg M14 anchor nut for an OS repair to an M12 bolt hole, ended up making our own (gear leg mounting holes didn't match the spar jig, so they taped off the hole in the jig before issuing the job with it noted in the work package, but put a new guy on the job each time for each spar, we issued the same concession 5 times till we ran out of gear legs).

Last time I encountered the "we should use metric hardware on role kit because the airframe is metric" problem, the quoted hardware prices caused us to go with imperial.

Eurocopter is the biggest user of metric hardware I have encountered. I have just done a quick skim the "additional supply manual" can't see any M5.5 anchor nuts.

 

[Sparweb]

I think somebody's sent you out looking for a skyhook. Or a bucket of steam. Don't feel bad, your rookie years will soon be behind you.

Good luck finding these:
NA0027/NA0028 - Nut, Self locking, Floating, Plate, Two Lug, Metric, Low height

I also have no idea who came up with "M5.5" but it sounds like someone making damn sure it's impossible as hard as they possibly can.
At least try to select thread forms that are common before hunting for fastener types that aren't common.
Refer to FED-STD-H28/21 for metric thread forms used for fasteners you can actually procure.

Is this "M5.5" fastener hole blind tapped (making it difficult to alter) or is it just a clearance hole that happens to be 5.5 mm diameter?
If the latter, well any old #10 screw will fit, if a bit loosely.

 

[MintJulep]

Is it just a 5.5 mm diameter hole, intended to have an M5 threaded fastener through it?

M5 nut plates, rivet or adhesive mounted are available from a couple of sources.

I guessed that a/nut was an adhesive mounted nut plate, because Clickbond makes such things.

 

[rb1957]

yes, "a/nut" means anchor nut.
yes, "M5.5" is the screw hole (complete with 90deg CSK, sigh)
"Don't feel bad, your rookie years will soon be behind you." ... NP, I'm well into my second childhood !? (just a few years ahead of you, Steve !)
yes, we've found the adhesive Clickbond a/nuts ... but I can't believe there are "no" metric riveted a/nuts (that's what I'm being told).
"Fastenal" ... ok, nuts of all types (but I don't see "anchor nuts" on their site ?). Do they give "aircraft" CofCs ?? (they look like a general construction hardware site).
Still not sure if I've reached someone on the other (European) side of the pond ?


"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

Personally I think that SparWeb 13 Apr 23 04:18 summarized Your dilemma.

So... have You contacted the antenna OEM for their hardware install recommendations???? Their antenna... so install has to be their problem also.

Perhaps, after You have designed the interface spacer [assuming curved/compound-curved install surface], the tacky-urethane/wire conductive gaskets, any interior hole reinforcement doubler(s) etc... then it's the OEM's obligation to advise/recommend available/common bolts/washers/nuts/nutplates that 'play well' with their antenna.

Better, yet, suggest you have the OEM provide an 'install kit'... gasket + hardware + canon-plug(s), instructions, +spares/excess etc... for Your installs!!!

NOTE: There are 'creative' options for installing this antenna using common US hardware... but that option info is/are for another posting.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

thx, but in my experience antenna people would probably suggest a basic nut (which would be a PITA in the field, compared to an a/nut). We can use clickbonds ... it is a messy, dirty environment (in the tailcone, beside the ACMs and such, but easy access if a nut disbonds. We can also cover (liberally) with PRC.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[MintJulep]

When you write "M5.5" it's a thread call out. Incomplete, because the pitch is missing, but still, the "M" identifies it as a thread.

That, plus the "a/nut"jargon that none of us understood are probably much of your problem - people don't understand what you're asking for.

If you have a 5.5 mm diameter hole, and you want to stick an M5 threaded fastener through it and screw that into a nut plate it's a much easier thing to find.

https://www.rotaloc.com/products/bonding-fasteners/female-nut

https://catalog.howmetfasteners.com...-metric-nut-plate-rivetless-standard-floating

http://www.weldmountsystem.com/products-fasteners-standoffs.php

https://www.specialityfasteners.in/self-locking-nuts-and-nut-plates.html

 

[rb1957]

thx, howmet looked promising. Not sure I want to risk "India".

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

RB... I ran a few numbers...

5.5mm [= 0.217-in Dia hole]. I checked NA0060-050 FTH Bolt and the shank Dia is 4.965-to-4.990-mm [next diameter is 060 = 5.965-to-5.990-mm]

5.500D hole - 4.965D-shank [mm] = 0.535-mm = 0.021-inch clearance.... SLOPPY!

SOooooooo... it looks like....

Any common NASxxxx Flush Tension Head [FTH] Bolt [steel, A286 or titanium] 3/16X... 1st-OS [+0.0156]Dia... is ~0.2021-to-0.2026-inch Dia... will install with a slight clearance fit of 0.217 - 0.2021 = 0.017-inch clearance... less sloppy.

Suggest You use US standard, commonly available parts ... 3/16X + Nominal 3/16 nutplates.

Sorry can't help myself...KISS.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

yes, but I have a metric (90deg) CSK. yes, I know the difference is small but I can't stop myself hearing the Mayday presenter ... "they installed imperial sized screws into a metric sized hole (or a metric screw into an imperial anchor nut) ... how sloppy can you get !!"

and yes, it may fit, but is it "right" ? and what allowables to use (yes, the loads are tiny, but ...) ??

for me "KISS" is metric screws and hardware to suit the metric hole and CSK).

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

OK... 90-Deg Csk??? which apparently CANNOT be tweaked to 100-deg by the user?

Stop the presses...

A 90-Deg Csk does NOT appear to be common for aerospace metric... 100-Deg appears common[?] as far as I can tell... so... is this an non-aero antenna being adapted to an aircraft?

I suppose a 90-Deg countersink filler + a protruding [pan-] head 3/16X PTH bolt is out of the question.

DANG. Shut-up Taylor.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

90 deg is (I'm told) typical for European screws, and the antenna bases come with them. I've suggested touching them to 100 degree (you probably couldn't tell the diffrence) but to borrow an English phrase "that's more than my job's worth" (oh no it isn't !!). Yes we could machine interface washers, yes we could machine our own screws ... many ways to skin cats (cats like none of them !). sigh

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Ng2020]

.217" dia corresponds reasonably well to a typical clearamce fit for a nominal 3/16" fastener. (Eg NAS619 hole limits for class "E") OEMs are similar, see your favourite SRM chapter 51.

Normally the antenna would have a tighter fit, with clearance fit + floating nutplates in the fuselage. But I guess it *could* be implemented the other way around.

Doesn't in any way solve your 90 deg csk problem though, but might lead to other ideas. Have fun.

 

[SwinnyGG]

90 deg is (I'm told) typical for European screws, and the antenna bases come with them

Do you aerospace guys seriously never ever deal with metric hardware?

90 degrees is the standard metric countersink.