One letter … come on! Some argue that the BC547A, BC547B, BC547C and C847-CK180N are “some transistor” and the letter suffixes are just a clerical trick to suggest an extremely wide product range from the manufacturers mainly for printing massive catalogues and confounding competitors. Indeed any of the three ‘547s will work satisfactorily in a lowly application like an electronic switch to turn a 20-mA LED on and off. The same for a uA741 and a (fictional) UCLM741CC12NDP8-56C; or the case of a colourful 1-kΩ resistor from the nearby component tray versus a device with MCP25RRS102 printed on it but only legible using a magnifying glass. All these parts will let you get away with their use in simple, undemanding applications and you may wonder why the ‘difficult ones’ exist in the first place. If you want to remain on the safe side in replicating a project or repairing a piece of electronics, stick with the exact specification of the designers as far as XXL part numbers go. If on the other hand .....