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The only difference is the radius of the curve to match the different size tubing they get attached to. If it fits, use it wherever you want.

A couple of questions related to the original post:

- is there any reason I can NOT braze / tig weld a rack boss on to a front fork?
example: REAR RACK BOSS LARGE (MTB) :: SMALL PARTS :: BRAZON/SMALL PARTS :: Nova Cycles Supply Inc.

I would prefer not to drill and press in / braze a standard front rack boss:
example: LOW RIDER BOSS :: LOWRIDER BOSSES :: RACK :: STEEL SMALL PARTS :: BRAZON/SMALL PARTS :: Nova Cycles Supply Inc.

Mainly I don't like the idea of drilling a fork that was not originally designed for the boss. I'm viewing that hole I just drilled a weakening the whole structure.
Also - any reason I cannot tig weld these bosses on?
I don't know how to braze or tig weld - so both cases are a learning experience for me.

The low rider boses silver brazed are a high success type deal. Tig welding, almost 100% that you will blow them through the fork.

TIG is reasonably difficult to learn if you are in someone else's shop, and their machine is set up for bikes, and they give you some tips. If you are going at it yourself, you are in a deal where you have many variables any one of which may queer the deal (flow too high, flow too low, etc...) and you can't easily tell which is wrong until you work through a lot of stuff.

As far as weakening the fork, this is the deal. You need to place the hole in the center of the blade, which is the neutral axis at least as far a major loads. You are in fact placing the hole in a place where the load from cornering peaks, but not to worry, the geometry on that axis is like a tube section the full width of the fork. While in the other axis it is 2xs the tube section of the individual fork blade. Strength and stiffness increase to the 2nd and 3rd power of the section so the structure is plenty strong on the transverse axis, one would like to think.

The second part is that once you braze or weld in the insert it is a flange to the tube that will form a safe alternative load path. So in that sense it is one case of minor BO adding where it would mater a little that you got the job right, with silver that is relatively easy first time out of the box with an proper torch.

As far as forks are concerned, Any reasonably sturdy fork is a candidate. There isn't any FEA going on with this stuff. Forks come in all shapes and sizes, if they are in the right range they can have these BOs installed, which pretty much means any not terribly expensive or light bike is a candidate.

While it doesn't solve your practice problem there are racks that use the brake boses as an additional fixture point.

You might want to consider that weight at the front doesn't handle well unless the fork is low trail..

I've used hour glass bosses mounted on end (to create a stand off) for low rider mounts. I liked that they would allow the rack upper side rails to be more parallel to each other. (Classic low rider racks like Blackburn or Eclipse had the front end of the side rails further apart then the real ends). I used silver and never drilled a hole or had any issues.

MassiveD - duly noted with TIG welding. I'll stick with the brazing I don't know how to do yet. And thanks for the good advice on drilling the fork. It's an '85ish Peugeout lead-pipe frame, so it probably thick enough to drill full of lightening holes. (kidding...)

Andrew - that's an interesting idea with the boss mounts - I was thinking of brazing the front of the fork into the curve of the braze on. But I can see how having the rack stand of would improve mounting a rack.

Thanks!

Bechman has a good detail for that which is welded into the fork, possibly side to side. I have a picture somewhere of that.