41763 is one part number purported to be from Lego for this. Another number purported to be from Lego for this, and only 3 digits, is 500. Another number for this part, frequently described as Lego's official number and found in three different Lego originated databases, including software named Brickfinder for theme park model makers, and Factory Lego Digital Designer (LDD) for public custom model creation, is 42023. The number 41763 may be correct but applicable to the part when it's made in transparent plastic.