I googled the question and one of the hits was from a well-known retailer, Tony's Trains. Note that I, personally, would NOT call these 'gentle' curves. They may have been yesteryear with smaller layouts and earlier rolling stock, but these days, with more realism, the importers specify somewhat larger radius curves for longer passenger cars, autoracks, that kind of thing:
The Peco ST-245 is a Setrack Code 100 Left Hand Curved Turnout designed for HO Scale model railroads. Let’s explore its specifications: