I have found details of a replacement worm for Bell & Howell projectors which may be of interest as it has details of its measurements. The video has a title "Fitting a new worm gear" but doesn't really seem to do this.
Unfortunately it says that the item has sold out but I am sure that similar ones are on the market.
Bell & Howell Worm Gear Page (ian-partridge.com)
Unfortunately it says that the item has sold out but I am sure that similar ones are on the market.
Bell & Howell Worm Gear Page (ian-partridge.com)