My heating oil tank contents gauge (at home not on the boat) has been broken. I'm trying to replace it. However I am stumped when deciding the nominal size of the threaded hole in the top of the tank in order to buy a replacement gauge. The diameter of the hole is approx 45mm. For reference purposes only, I measured the size of a spare wash basin waste I happened to have at home against the hole in the tank top. It is a good bit too small to fit the threaded hole and would drop into the tank, this waste fitting has a diameter (outside edge to edge of the thread) of about 41mm, the locking nut is 45mm (flat to flat of spanner size) and the internal diameter of the waste is 37mm. The box it came in claimed it to be a chrome plated 32mm waste. I understand that the welded-in threaded flange in the oil tank is a BSP size, either (I suspect) 1.5 inch or 2 inch, but from the above (probably useless) info. which size is it most likely to be? The gauge I would like to buy comes with a 1.5in BSP thread size only (and from the photo of it on t'internet it does look just like the one I'm replacing (vintage 1995)). A different (and much more expensive and sophisticated (more to go wrong)) gauge comes in 1.5 inch and 2 inch sizes. Arthur Naylor nb Housebound
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