You will need to make use of lineitem "options" param. You can attach as many options as you like using something like:

<input type="number" name="options[numberDistance]" step="any" placeholder="Add your minimum distance in mm..." id="distanceNum">

And then these will be avaliable on the lineItem once saved using

{{ item.options['numberDistance'] }}

You will need to make use of lineitem "options" param. You can attach as many options as you like using something like:

<input type="number" name="options[numberDistance]" step="any" placeholder="Add your minimum distance in mm..." id="distanceNum">

And then these will be avaliable on the lineItem once saved using

{{ item.options['numberDistance'] }}

More info can be found on the Craft Commerce docs