Originally Posted by
Salamandrine
...Could 5583 be the alloy? I know there is a 5083. Possibly more likely to be some production code...
I used to consider that possibility but have my doubts. However, it is almost certainly a JIS standards number, as it is always accompanied by the JIS symbol. JIS covers bicycles under the D (automotive) section of their standards. Consequently, I'm currently leaning to the it indicating D5583 and being a bicycle brake standard. Similarly, all the Suntour derailleur claws exhibit the JIS symbol and 4532, which I believe is actually D4532, a derailleur standard.