You are bidding a new old stock Thordarson Model 20C51 filter choke, with its original box. It is rated at 35 H, with DC resistence of 1850 ohms. It measures roughly 1 ¾ by 1 5/8 by 1 ¼ inches is size, not counting the mounting flanges. Is should be useful for a DIY tube amplifier. Shipping weight is 12 ounces. Please see my other auctions for more interesting tubes and radio/audio items!