The filter thread size of Tamron SP AF 17-50mm F2.8 XR Di II LD Aspherical IF is 67mm.
Below are links to the filters that we recommend you to consider for your Tamron 17-50mm f2.8 XR II LD:
Read our detailed Tamron SP AF 17-50mm F2.8 XR Di II LD Aspherical IF Review