The threaded portion of the shaft is 10mm x 1mm. However, where spinner goes on, the shaft steps up to 12mm OD without thread. So you need to ream your spinner to a 12mm hole. I wouldn't recommend drilling it, unless you have a drill press and can ensure centering of the enlargement.

Fox sells a 10mm & 12mm reamer, with a 1/4" pilot. So what I do is to insert a plastic sleeve with 1/4" ID and 9mm OD (comes with a lot of plastic spinners) so this reamer's pilot will be centered in Tru Turn spinner's 9mm existing hole.