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I just got a good deal on the luggage rails with rack off of Ebay but it doesn't come with hardware. I have the sizes M6X45MK, M6X35MK and M6X16A2. Not sure what the MK or the A2 stands for after the numbers stands for, and McMaster Carr doesn't list anything with those numbers. BMW Chicago has the first two (but I don't want to wait a month to mount these) I also have the BMW part numbers.

Can anyone clarify what those numbers mean, or let me know if I'd be okay getting M6X45 in stainless with the right type of head???

Thanks

Gary

Gary, I have no idea what those letters mean, but don't worry about it... I'm sure it's some screw class, or material, or something equally insignificant. If you were talking about replacing engine bolts than you'd probably want to make sure you had the correct class of bolt, but for a luggage rail just go out, buy what fits, and you're good to go. When I bought rails and a rack for my Rocks I just went to my local Sears Hardware and got the right size stainless steel screws... cause BMW prices for screws are nuts... ... get it, the prices on the screws are nuts...

I would imagine those other part letters are the stand-offs needed to mount the rails. There's 2 different sizes you will have to have to mount them properly.

-joe

A2 appears to be a grade of stainless steel. Here is a site:
http://www.boltdepot.com/Fastener-Infor ... Chart.aspx
that offers some info. As to what the MK signifies, ???

Hello,

as far as I remember A2 is stainless steel 304 (not good quality) and A4 is stainless steel 316 (good quality).

All metric bolts imported into the US were once required to be stamped with a code representing the manufacturer. I'm not sure if that's still the law, but it probably explains the "MK" designation. This traces back to a situation where some foreign (Chinese, IIRC) factories supplied sub-standard bolts to the US military.

The main differences between 304 (AKA 18-8 or A2) and 316 (A4) stainless steels are corrosion-resistance and cost. 316 is used for marine applications and are much more expensive. There is no difference in terms of tensile strength, and both should be OK on motorcycles.

It's also worth noting that all stainless steel bolts are weaker than SAE grade 5/metric class 8.8 plain steel bolts. So don't substitute stainless for plain steel just for the appearance unless you're sure the application doesn't require the increased strength.

ChiTown wrote:I would imagine those other part letters are the stand-offs needed to mount the rails. There's 2 different sizes you will have to have to mount them properly.

-joe

I see no stand offs in this diagram that you mention. The assembly is all put together, it was a take off from a wrecked bike, so all I can see is what I need to mount it to my bike.

http://www.realoem.com/bmw/showparts.do ... g=46&fg=20

alaskaflyer wrote: I see no stand offs in this diagram that you mention. The assembly is all put together, it was a take off from a wrecked bike, so all I can see is what I need to mount it to my bike.

http://www.realoem.com/bmw/showparts.do ... g=46&fg=20

you are correct, there are no stand offs in the diagram. Weird that they aren't there...

There are small metal tubes that the screws go through to the mount the rails to the frame - stand offs or whatever you want to call it. There are at least 2 different lengths, and they can fall out of the rails easily, most of them fell out when I swapped out my rails for the non-rack ones.
Hopefully yours will have them still in it, but if there's no metal tubes in the rails then you'll want to get some. I see them as being very important to mount the rail securely.
Now if you have the non-tail rack rails that allow you to mount hard bags, you might have what you need already...

What are you planning on using the rack for?
I see having rated bolts as being a good thing for this application, at least if you put as much weight as I do on my rack... I've bent the 2 closest to the rear one just slightly and the BMW one's seems like they are hardened. Home Depot hardware might not have the strength to withstand that stress.

-Joe

I plan on using a higher grade bolt. I've always used one up when I work on my trucks or bikes, just having that sense of security.

Thanks for the info on the sleeves.

Gary

BMW uses torx fasteners on the newer machines. But any ISO metric fastener of the correct size will fit. Black metric torx fasteners will be difficult to find. Go to good hardware store and get some 6mm allen cap screws, the zinc plated ones will not rust, you can always paint them black. For a cool look you can get stainless metric button head screws with a allen hex. You don't need grade 8 bolts to hold bag mounts, or a luggage rack. Most stainless fasteners are of a grade 5 quality. They assemble HD's with grade 5 fasteners and parts don't fall off of them.

motoracer8 wrote:Most stainless fasteners are of a grade 5 quality.

Not true. Grade 5 fasteners have a tensile strength of 120,000 psi, roughly equivalent to metric class 8.8 at 116,000 psi. Stainless metric fasteners (A2 or A4 alloy) are only good to 75,000 psi. That's a big difference.

In general, it's not a good idea to switch to a weaker bolt unless you're sure the application will allow it. Engineers usually select the minimum strength required to do the job (plus a moderate safety factor); using a weaker bolt may well give up more than that safety factor.

Neil, You are correct about general stainless hardware, but I buy grade 5 stainless nuts, and bolts from England for my British bike projects, they have standard sae thread pitches and have the three marks to indacate grade 5. I'm not shure of the maker, but they are stamped GKN-SS on the bolt head along with the hash marks. The OE hardware that comes with the BMW bag mounts/ luggage rack, are stainless, quality unknown, 6mm, 1.0 thread pitch torx flange head screws. I would bet BMW will charge plenty for these 8 bolts. The bag mount rails and rack are plastic, standard metric hardware will be fine. The holes in the mounts/rack should have steel spacers in each one so the bolt does not crush the plastic on assembly.

Ken G.

Ves wrote: ... get it, the prices on the screws are nuts...

Please advise what you are drinking... I can use some myself

motoracer8 wrote:...They assemble HD's .....and parts don't fall off of them.

A lot of my HD riding buddies would argue that point with you !

ka5ysy wrote:

motoracer8 wrote:...They assemble HD's .....and parts don't fall off of them.

A lot of my HD riding buddies would argue that point with you !

Strange, nothing fell off of my HD in three years of riding. I was pleasantly surprised, amazed, actually, at how well put together it was.