The Model 37 Classic Slide tube features a threaded nut on the rear and a bar Heliarc welded to the tube. This tube has been on most Model 37s throughout the years of manufacturing. ****Different years of manufacturing require different lengths of the tube. To ensure proper fit, please refer to the length descriptions before proceeding. The out-of-stock parts can be made by Ithaca, but require the actual wood forend, original tube, and nut to be sent to Ithaca Service for proper fitting.