This SIGMA-made lens has a Sony E (NEX) mount. If you want to use a filter on the lens, then the filter size is 55 mm.
From London Camera Exchange
Sigma 17mm F4 DG DN | Contemporary - Sony E-Mount
Harrison Cameras
Sigma 17mm F4 DG DN Contemporary Lens - Sony E Mount
This product is also available at 1 unverified store.