Numeric Fields not linkable

Hi -and sorry for blitzing things today. I added a custom field called member_id as I just wanted a number but accidentally added it as a text field.

I then selected that as the link field from the List page to the single page. I noticed though, that the sort was weird and then realised it was an alpha sort (so, 1, 10, 11, 12, 2, 3 etc.)

So, I changed the definition of the field to numeric but now it doesn’t list that field in the drop down t oselect the link field. Is that correct?

Many Thanks