Thanks for your question! The numbers indicate a chainÕs dimensions, tolerances, minimum tensile strength and other specifications, using a system instituted by the Japanese Industrial Standards Committee. The JIS standard is very similar to chain standards developed by ISO, ANSI, DIN and others.
The first digit (4, 5 or 6) denotes a chainÕs pitch Ð the center-to-center distance between chain pins. Originally these numbers specified pitch in eighths of an inch (i.e. a 400-series chain had a pitch of 4/8, or 1/2 inch), but now metric dimensions are used. A 400-series chain has a pitch of 12.7mm. A 500-series chain has a pitch of 15.875mm. A 600-series chain has a pitch of 19.05mm.
The second and third digits indicate the chainÕs width, measured between the inboard surfaces of the inner sideplates. An EK chain ending in Ô20Õ measures 6.35mm between the plates. If the number ends in Ô25Õ or Ô28Õ, the dimension is 7.94mm. If the number ends in Ô30Õ or Ô32Õ, the width is 9.53mm.
Because wider chains are typically stronger as well, the second and third digits also indicate a chainÕs strength, relative to other chains with the same pitch. Higher numbers correspond to greater strength, i.e. a 525 chain is stronger than a 520. This additional strength is achieved through increased roller diameter, pin diameter, pin length and plate thickness.
You should always replace your old chain with one having the same JIS number. Never replace a sealed chain with a non-sealed chain
Answered on 10/28/2009 by SalesDepartment