1) Determine size; .125 ? .150 ? Did you sixe sample enough to determine if they used different sizes to eliminate backlash.
2) Determine manufacture: they should help you with the numbers if it is a standarded loaded ball screw .
3)If you can not determine manufacture, then go to www.rockfordballscrew.com,click on their service manual...then click on assembly of a Standard Ball Screws..by following these instructions you can correctly "stuff" the ball nut to full. Using a lathe chuck to hold the screw while loading sure helps (along with vasoline,no phone , no kids and no significant other bugging you )
4) By experiance only, I have found that you can use a ball nut .0003 to .0005 oversize to eliminate back lash( if the nut and screw are in good shape) if that was the original intent to unload the ball nut.If accidental, and no damage is evident in the ball screw or interior of the nut, use the ones it came with.
5) The "start" and "finish" threads of different ball screw manufactures are all different.The active threads only include those that are between the start and finish of the return tube.Loading balls "above" the start of the return tube traps those balls without benifit of circulation.Loading "below" the start and return will only spit the balls out when you rotate.
6) other than that , ball screw loading is an art, more than a science, and good luck !
Adobe (old as dirt)