Sounds like you've separated the two halves of the angle adapter. :
Put the bolt through the bit you turn to tighten the adapter, then through one half of the adjuster. Put the nut in the other half of the adjuster and then you can turn the tightener to screw the bolt into the nut. Hold both bolt and nut in place until the threads bite.
Next time unscrew the brush head from the end of the adjustable angle :