4 inch Extension tube for FLT seriesWilliam Optics 4" Extension tube for FLT series. William Optics 4" Extension tube for FLT 98,FLT 110 and FLT 132 telescopes is very useful if you use a CCD or need more drawtube extension but still expect flexure in your train. The William Optics 4" Extension tube is fully anodized, and compatible with other similar telescopes. To mount the William Optics 4" Extension Tube on the telescopes, simply remove the 4" nosepiece adapter for the telescope and