On Fri, 29 Apr 2016 07:10:55 +0200, Emanuel Berg
wrote:

On a bicycle trailer, facing outward, the wheel axle
fits into a hole. Here, the dome nut is free so most
tools will do. On the other, inward side, there isn't
a hole but a horizontal gap. Here, there isn't a lot
of space so a socket wrench or ratchet I suppose
is preferrable.

1) Is there a reason for the gap (instead of hole),
like room to adjust after an injury to the frame,
or so?

I'm not sure you explained that sufficiently, but if you mean that the
outboard end of the axle is aligned by fitting through a hole and the
inboard end fits in a slot and can be wiggled back and forth I would
guess that is an design feature which is intended to allow for sloppy
fit ups and misalignment during manufacture.


And 2), is there a method how to get the wheel plain
straight? No matter how careful I do it, it seems
I pull the axle a little bit out of the original
alignment with that last pull to seal it.

Very careful twisting the wrench :-) That is a joke but essentially
true. You will need to learn how to tighten a nut/bolt by twisting
only, no pulling on long wrench handles which dislocates things.

3) Speaking of dome nuts, some have grooves, if that
means you don't use a washer, what has more strength,
plain + washer or just grooves?

By "grooves" I assume that you mean grooves on the face of the nut as
an anti-loosen feature, but that doesn't have anything to do with the
strength of the nut-axle joining which would be a feature of the nut
and axle thread engagement.


Thanks for all your help.
--

Cheers,

John B.