It's more complicated when it comes to choosing the right channel!
I'll try to help you out a bit.
The first thing to know is the size of the chain. In the world of motocross there are 1 sizes. The 4, the 415, the 420 and the 428. It is simply the size of the links.
The 2nd thing that is good to know is the length needed. This is why we often see the chains described as follows: 520-120, 428-136, 420-130, 415-110. The 1st number is the size of the link and the 2nd number is the total number of links in the chain.
From my side, I offer you longer chains because it is easier to shorten a chain than to lengthen it.
The 3rd thing to know is for which application. A 520 chain for a 450cc motocross can still be installed on a 125cc but I would advise against the reverse. The difference is this; tensile or stretch resistance. You have to take care to choose well when buying a chain because it is really important. It should be written as follows: Supports 6500lb / ft (example)
This is why there is so much difference in price from one chain model to another for the same chain size, which is the 520 in my example.
If you take an entry level chain and install it on a 450cc for example, you will spend your time adjusting it or even worse it will break and could damage the engine casing, near the front sprocket, with the rotational force of the motor.
You don't have to go through this, I guarantee.
The 4th and last thing is whether you want with or without O'ring? What are these O'rings again?
These are small rubber gasket installed on each link-link of the chain. Thus preventing water and mud from entering the links and creating premature wear.
O'ring chains are more often used by enduro-cross riders because the chain is put to the test in this discipline. The advantage, too, is that the O'ring chain often has a better tensile strength index. The downside is that the chain is often heavier, making it more difficult for a small cylinder to twist the chain, causing quite simply a loss of power.
This is why on a motocross circuit like MXPN, we often offer a chain without O'ring on a small displacement motocross.
Thus, we leave the motocross to its optimal performance.
Here is my little training on the chains.
Still not sure which channel to choose, use my Parts Finder and I will help you!