chain sizes! or whats up with all these numbers?

[pbeggs]

Chain Number	Pitch	Roller Dia	width	Pin Dia
#40 (#425)	1/2	.312		5/16	.156
#41        	1/2	.306		1/4	.141
#410 (#43)	1/2	.306		1/8	.141
#415 (#42)	1/2	.306		3/16	.141
#415H (#42H)	1/2	.306		3/16	.141
#420		1/2	.306		1/4	.156
#25		1/4	.130		1/8	.091
#35		3/8	.200		3/16	.141

here is a chain size guide
this refers to us chain size,.. not the metric chain that can come as motor chain for some chinese 2 stroke kits (best replacement is #41)
chain numbers in () are industrial chain numbers if diff.

information is from this website http://www.azusaeng.com/chain/mcyclchn.html