The numbers used in chain sizing are all in 5/8ths on an inch. The first number is the pitch (the spacing between the pin centres) and the other two are for the width of the chain.

The first number is the pitch, the spacing between pins.

• 4xx = 4/8" = 1/2" pitch
• 5xx = 5/8" pitch
• 6xx = 6/8" = 3/4" pitch

The 2nd number is the spacing between the plates, the chain width

• x20 = 2/8" = 1/4"
• x25 = 5/16" ( (2/8) + (0.5 or 1/2 of 1/8) = 2.5/8 = 5/16")
• x30 = 3/8"

Therefore a 530 chain has a 5/8th inch pitch and a width of 3/8"

A 520 chain has a 5/8th inch pitch and a width of 1/4"