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The new Motobins R series bolt is marked 50 - its length.
The old stretched only has the number 6 or 9 , no decimal point
or other digits.
Maybe from a later model paralever according to
vanzen@rockerboxer.com

Those black bolts (cap screws) have a bigger problem - they are not the shoulder screws that are specific to this application.
Make sure that the screws you are using are not threaded all the way to the head. That unthreaded section must be present to mate with the hole, and to prevent the stretch you encountered.
Cheers,
Jon-Lars

r90s wrote:Those black bolts (cap screws) have a bigger problem - they are not the shoulder screws that are specific to this application.
Make sure that the screws you are using are not threaded all the way to the head. That unthreaded section must be present to mate with the hole, and to prevent the stretch you encountered.
Cheers,
Jon-Lars

I hear what you are saying, but I do not understand ... so I am asking ...
How would a full-threaded screw behave any differently from a "shouldered" screw
IF the 2 screws are of the same tensile strength rating ?
Certainly the (marginal) difference in O.D. could not be a significant factor as both will have the same tensile rating ?
Given that the ISO rating is the same, the applied torque is the same, the applied stress is the same,
and the evidenced distortion is not a function of incorrect "fit" ...
I can only see two scenarios: An inappropriate rating of the distorted screw,
or negligence in the way of improper torque on a correct screw.
My bet is on the latter.
What am I missing ?

Hey Jon, good to hear from you. Don't be a stranger.

That's a good point, Vanzen.

Do you know the tensile strength of the BMW product?

Anyway, shoulder screws are used - as is the case here, in effect - when shear strength is required. That is, the force applied to the screw shaft is perpendicular, as if to cut it in half, instead of pulling it out.

Having threads in that part of the screw shaft reduces the root diameter, and the yield strength, of the screw. Also, the threads may wear into walls of the hole of which it is fitted.

r90s wrote:That's a good point, Vanzen.

Do you know the tensile strength of the BMW product?

European auto "lug bolts" ('Merikans seem to favor studs & nuts) are typically ISO 10.9,
I can only assume the BMW mc item would be similar, as there are no markings to verify.
I wonder if BMW auto "lug bolts" will have the same (angle of) taper as used on the mc mono hub ?

r90s wrote:Anyway, shoulder screws are used - as is the case here, in effect - when shear strength is required. That is, the force applied to the screw shaft is perpendicular, as if to cut it in half, instead of pulling it out.

True, however. the distorted screw pictured shows evidence of "pulling" or "stretching", but not shear.
I'll need to do some digging to find if shear strength will be = between the two ...

r90s wrote:Having threads in that part of the screw shaft reduces the root diameter, and the yield strength, of the screw. Also, the threads may wear into walls of the hole of which it is fitted.

The screw's shoulder does not contact the hub as far as I can tell.
It, in fact, fits rather loosely in the hub if it is inserted without it's associated "cone".
"Bearing" will be provided by he rather large surface area of contact of this cone fitted behind the fastener
and the tapered portion of the drilling in the hub, and guaranteed by proper torque of the fastener.
The cones, of course, also center the wheel to the hub.

I have been interested in these issues since no stock BMW mc lug screws will fit CRo's hub / wheel combination.
and ISO 10.9, M12 x 43 - 1.5 screws are not to be found.

What's the latest on your project, Vanzen? Maybe you have a thread on here somewhere?

Is there some reason to not use the stock screws on the rear? Too short or too long?

I'd want to examine the threads in the hub, very carefully.

r90s wrote:What's the latest on your project, Vanzen? Maybe you have a thread on here somewhere?

Some info here:
http://boxerworks.com/forum/viewtopic.php?f=3&t=656

r90s wrote:...
Is there some reason to not use the stock screws on the rear? Too short or too long?

Stock issue screws are too long at 50 mm.
With a K75 final and modified Paralever GS hub, I need a length of 43 mm.
The stock fasteners can be made to fit, of course.
This would involve cutting to length and extending the threads further up the shoulder.
The work seemed excessive – until I found that 10.9, M12 x 45-1.5 screws are unobtanium
unless an order of 100 is needed.
(45 mm being closest to the 43 mm and having an appropriate length shoulder–
but would also need to be shortened)