sprocket?

Hello guys, I am building my first Cafe racer from a KZ400 1980, and I have some Ninja 250R 2008-2010 wheels and swingarm, Therefore I need a new rear sprocket.
The sprocket on the KZ are 44 teeth and the marking on it is 44Z 0476, That my first build, and I have not found what the last 4 digits number mean. I wish to keep the same ratio.

Some perhaps dumb questions:
are the standard for sprocket the same, in term of x number of teeth equal the sprocket diameter, so a 44 teeth kz sprocket will be the same diameter of a 44 teeth 250R sprocket? I just want to make sure.

Secondly, I wish to keep the same chain, are those standard so I can order a custom one? and therefore I guess the new sprocket should be the same thickness as the old one???

Thirdly, Is that the easiest way of doing it? as perhaps it is easier to find a front sprocket rather than the rear?

Thank you in advance for your help.
Erwan

Measure the chain to see what size it is (see link below for details). Once you know the chain size order sprockets for that size chain, and just order the number of teeth to match the ratio you want. So if your old front sprocket (called the engine or counter sprocket) has X number of teeth and the rear sprocket has Y number of teeth just buy sprockets with the same number of teeth in the sprocket size that matches the chain size. Also, it is wise to replace both sprockets and the chain at the same time. Otherwise the chain and/or sprockets will wear out prematurely. Ed

www.moto-chains.com/site/898528/page/578189