SN1770-Z Zoom Gear ~for Sigma 17-70mm F2.8-4.5 DC Macro HSMZoom gears allow access to the mechanical zoom function of supported lenses. Use of this gear may require the use of additional port extensions or adapters. Check the Port Chart for more details. This zoom gear is for the Sigma 17 70mm F2. 8 4. 5 DC Macro HSM (Nikon mount) lens. This item is non returnable, non refundable, non cancellable, and may be subject to extended lead times as it is manufactured on demand. We always do our best to meet trip