The front wheel guard brackets on my Luego Velocity are supposed to fit onto the ball joint threads, there is only one or two threads to tighten the nut up against.

Any suggestions would help

Math

Not sure if it helps, but if they are like the ones I had on my Westy with Cortina uprights, I had to grind a bit of the upright away so the bracket fitted on with enough space to do up the nut.

Think if you do a search this has been covered several times. It seems that some makes of Transit joint have shorter threads than others. HTH